My Chevy Lumina will not start hot, runs/idles rough
I have a 1996 Chevy Lumina LS, 3.1 V6. Over the last 18 months I have had problems with it getting hot (not engine coolant) and not starting after driving for a while or running a few errands of 10-20 miles round trip. Sometimes it will start up and idle rough and I can coax it into running. The "service engine soon" light comes on for a day or so and then goes out on its own. It is worse in warm/hot/humid times than colder weather.
I have replaced the plugs, plug wires, the 3 ignition coil packs, the coil pack that the 3 separate packs mount on, catalytic converter, fuel filter, cam shaft sensor. The problem is not as bad now as when it first began. However, it is still unresolved. The vehicle has 140, 800 miles. I am the second owner, having purchased it in 2007 with 65K miles on it.
Other than this, the only problem I've had was a water pump replacement. Does anyone know what to do/check? I've talked with several mechanics and get different stories from each. HELP!
Bryan he said he replaced the ICM. Darryl have you replaced the crank position sensor? Also have you had the codes read?
John, the latest thing replaced was the cam shaft sensor (think this was it), it could have been the crank shaft sensor. The codes have been read continually! The main thing is that there is a misfire. I am engine-savy enough to know that it is misfiring, just cannot find out what is causing. Thanks for the responses, any others things that I might suggest, checkout?
define "had problems with it getting hot". Have the ECT (engine coolant tempreature sensor) checked. If the car thinks its -40 degrees it wont run right.
Andrew, that's yet another sensor that has been mentioned that would need to be checked.
Also Andrew, there is plenty of coolant, hoses are good, etc. It is as if the heat generated by the engine just causes some type of problem. When it acts up, I raise the hood, let it sit like that for 30-60 minutes and it cools down and will run good until it does it again as noted previously.
Its an obd 2 so if its misfiring then the check engine light will flash. What did the codes read?
John, the people that have read the codes have not told me specifically which/what code was listed. So, I do not know that answer. The "Check/Service Engine Soon" light does not flash. It will come on and remain until the codes are cleared or as has been the case as of recent, it will come on and go off within a day. It came on on Sunday evening 9/23 and was off by the afternoon of 9/24. I am hoping to check the IAC, EGR & MAF sometime this week. Those are the things that have been suggested. Would AutoZone or establishment such as that be able to read the codes (at no cost) and let me know the specific code listed? Thanks for the information!
Yes auto zone and advanced both have the tool and do it at no cost around here (NW Indiana) and I believer everywhere in America. I assumed when you said you had them read that that's where you had irlt done. Make sure you get the code number and I can send you the procedure from a chiltons manual to diagnose it.
John I will do that, have read and post code here. Even if the "Check/Service Engine Soon" light has gone off (on it's own), will the fault code still be there (readable)?
John, I had the code/s read on Tuesday. This was from where the "Service Engine Light" had been on from Sunday until Monday. The code was P0171. The guy at AutoZone said it was some type of 02 sensor. Any help in this is greatly appreciated.
Code translates to 02 sensor bank 1 lean condition. It's odd becasue it's only one bank and not both. Could be defective o2 sensor, could be a clogged injector. If it runs good when cold it shouldn't be an injector problem. Untill the car warms up it doesnt use the readings from the o2 sensor, but when it warms up it will and if that sensor reads extreme lean it will tell that bank to dump more and more fuel till it maxes out and will run like crap. Makes sense to me, could be worth a shot to change it. I would use my scan tool to see how the o2 fluctuates if at all but I dont expect everyone to have access to one.
Thanks Andrew. I do not have access to the scan tool. Where is this o2 sensor located? What level of difficulty would you rate it (1-10, 10 being most difficult) to locate/replace this sensor? Thanks again.
decided to pull out chilton's manual, my gf had a 98 lumina so i bought the book. Luck for you. Says p0171 is system lean. Also found out there is only 1 o2 sensor. Opening up possibilities of vacuum leak or MAF sesnor. The o2 sensor seems to be accesible from the back of the engine between engine and firewall on the exhaust. Judging from your symptoms the MAF would also make sense. Having someone check your vacuum pressure should be easy and rule one thing out. The o2 seems kinda hard, if your not used to turning a wrench then it may be too challenging. It also requires a special o2 socket.
Thanks again Andrew. I am somewhat handy turning wrenches/sockets. Sadly some nerve damage in the hands does cause problems now though. Would cleaning the MAF be a somewhat simple & easy step to see if that might help any? And I am certain that I do not have the special o2 socket. Thanks again!
As far as the socket goes its pretty much a waste. Its supposed to make removing the old one easy and its an over priced novelty socket. To remove the old O2 sensor cut the wires and put a regular socket on it. To put the new one on use an open end wrench. That socket is just as silly as a snuggie. Andrew does your book cover anything older than a 96?
You can try cleaning it, be careful and use only approved cleaner. I've never had success out of doing it but some have. If there is any way you could gain access to a scan tool to read sensor outputs to figure things out quickly. I dont want to lead you on a parts changing spree.
My book is a 95-05 Lumina, Monte Carlo, and Impala. Covers OBD1 and OBD2 for these cars
and it seems the lack of space may make a wrench difficult to use otherwise i would recommend it as well. Sorry for the triple post
John & Andrew, both of you are being very helpful. While I can do a portion of this, specialty tools would cause a problem as would scan tools, etc. I did see that CRC makes a cleaner specifically for the MAF. AutoZone is listed as a retailer that carries the item. I appreciate the "not wanting to lead me on a parts changing spree" comment. As we all know, that may not resolve a problem and can get real pricey real quick! Thanks again guys!
Which is a better manual to purchase guys; Chilton, Haynes (sp), other? Thanks again!
I dont have an opinion, which ever is accessible. I made a typo, I have a Haynes manual, not Chiltons. Been so used to saying Chiltons I never bothered to look.
I have both and after goin to Lincoln tech I gained access to chiltons online which has pretty much every book on it back to the 60s and some from before that. I like the chiltons because it seems to have better wiring diagrams and helpful pics too Andrew the reason I'm asking is because the online chiltons showed pics all the way back to 89 with the old iron duke 2.5 and as of 1996 OBD 2 was required to be on every car sold in the USA and with obd 2 comes up stream and down stream sensors. So any American v6 as of 1996 and up will have a minimum of 3 sensors. Bank 1 sensor 1, bank 2 sensor 1, bank 1 sensor 2, these are required for the obd 2 emissions setups.
OK John & Andrew, now you're getting into technical lingo that is over my head! Give me the old carb engine, etc. and I am do the work. With all of the computer/electronic garbage on the new/er vehicles, I can get overwhelmed! My first car was a 1970 Chevy Impala Sedan; 350, 300HP tubo-fire! What a tank! So easy to work on!
I thought it would have 2 upstream but i havent been able to find evidence of a Bank 2 sensor anywhere. If you prove me wrong that would be great becasue that would make troubleshooting easier and localize 1 side but I cant find anything of it. Maybe it is after the exhaust meets but before the cat? GM liked making short cuts to cut costs. Being a 96 early on into OBD2 fits the bill.
Would you mind clarifying OBD1 & OBD2 guys?
I can see them going cost effective but there is definitely a downstream sensor i know my buddies 95 camaro v6 has an obd 2 plug and 3 sensors but since the lumina is a transverse it may have only 1 upstream. The 96 3.8 definitely has 2 upstrrams though and without having the car in front of either one of us with a scanner to read the live data its hard to say. Darryl obd is OnBoard Diagnostics and the 1 and 2 are can be compared to a computers operating system. OBD 2 is way more complex and the computer goes from controlling most things to everything. The newer cars when hooked up to the top of the line scanners like a snap on modis can amaze anyone unfamiliar with them. The computer can activate the horn, lights, windows on some models. The newest cars it can start the engine because when you turn the key to the start position the computer turns it on. You can turn it to start and immediately let go and the car will start on its own and if its running already the starter won't engage. The computer controls how much the throttle opens when you hit the gas pedal instead of a cable. The list goes on and on and here is a huge benefit from this technology. http://www.youtube.com/ watch?v=ZIIM8rw0au8
John,thanks yet again! As I noted, while I am not even 50 years old, I am more familiar and comfortable with the old carb-type engines (computer/electronicless ones)! Those were some real hosses and could be worked on effectively and correctly without all of these devices (computers) and having to read DTCs. I know of an older guy who was a mechanic all of his working life. He could listen to an engine and positively tell you what was wrong! That is what I miss so much! Thanks again. I will attempt to clean the MAF today and see what that does.
Its because of that technology we have a camaro v6 with 305 horsepower and getting nearly 30 mpg
Not disputing the technological advances there John. However, the 1946 Tucker was well ahead of it's time! The BIG 3 fought diligently to make sure that it never made it. On another note, I cleaned the MAF today. I noticed on the plates of the throttle body that the plate is gunked up some. Is this difficult to clean? Could it be part of my problem? As I was driving the car after cleaning the MAF, within two miles of driving, the "Service Engine Soon" light came on. I will try to have the code read on Thursday to see what code is being given now!! HELP!
Does your exhaust smell rich? Pull the accesible spark plugs and see if they are black with soot, saturated, or ashy. Tring to tell if the car is actually running lean or the o2 is lying and running rich.
Haven't smelled anything on the exhaust Andrew. I'll have to check the plugs on Friday. The funny thing about the light on Wednesday night; on my trip Thursday morning, it went off. I still went to see if the code could be read. It was readable. Again it was P0171. The guys at AutoZone give me the printout that lists 3 possible problems: 1) o2 Sensor (they say there are three of those; two upstream and one downstream), 2) Ignition misfire (doubtful on this as the 3 coil packs and ignition module have all been replaced), and 3) Fuel injector problem. They priced the injectors at $84 each, OUCH! Thoughts?
A bad injector would cause a misfire because for the engine to run lean the injector would have to be stuck shut drying out the cylinder and a misfire would cause the check engine light to flash reading code P0300-P0306. The only thing the auto zone employees know is what the computer tells the and the only thing the computer knows is how to look up parts. Since its a lean issue and its only on the one side I would venture to guess its a 75% chance of it being the sensor. If auto zone is correct and it has 2 upstream sensors simply swap them and see if the code changes to the other side. If the code moves its definitely the sensor.
Thanks John! What should the sensors be wrapped with to avoid any potential fire hazards?
My bad, poor vision in reading....swap, NOT wrap!
Hey guys hope you dont mind me butting in but im having the exact same problem and reading the exact same code however advanced auto told me my 97 lumina 3.1 only has 1 upstream o2 sensor is this correct or am i just not finding the second? The one ive found is just below the manifold in front of the fire wall? Would appreciate any input! Thanks
Its a lot to read but somewhere up there Andrew mentioned that around those years GM took a shortcut on some of their front wheel drive V6s and only put the one and what you said proves exactly what I said about auto zone only knowing what the computer says even when the car is in front of them. One store says one thing and another says another. Its most likely a universal thing and its since all the GM O2 sensors are the same the one computer has it listed as a part available. Every auto zone and advanced I have ever been to also lists a power steering pump for a Pontiac fiero.
Thanks so much for your time and information i bought one today going to put it on saturday REALLY hope this fixes my problem such a great car to be only able to drive when cold lol
Have we ruled out vacuum leaks?
Just visually, haven't had a test ran on it.
I dont know if you've read my earlier posts or if they make any difference but the problem is starting the engine when its hot it like its loading up its difficult to coax it into leveling on out but if your able to ( usually takes a few munutes) your good to go, if not and it dies on your stuck where ever your at until the engine temp has almost completely dropped to regular outside temperature. In either case wither you make it get right by coaxing it or you've started it cold, once running it never misses a beat at all i mean it runs like a top.
Im no car expert if i was id be giving advise instead of seeking it but i feel like whatever the problem is its got to be something that id call 'silly' just not sure what that is yet lol thanks for yals help though im very grateful
I would try the o2, and reading your post just answered my question. A vaccum leak would show it's head for sure at idle. Its also completly possible a sensor like the MAF messes up when it's hot and not when cool
Ok if the o2 doesn't work ill go that route. I noticed you dont recommend cleaning those or atleast havent had luck cleaning them. I bought what advanced said was the upstream see earlier that John said they are all the same my question now is whether the senors are or arent the same which one ( up or down stream) would most likely be my culprit ?
Nater said his has only 1 and his auto zone lists only 1 so I would say no, vacuum leaks are not off the table and since the intake is aluminium the expansion rate is different from the rest of the engine there may be a vacuum leak on an old hose or at the intake. A logical possibility is as the engine warms up the vacuum leak gets gradually worse. As this is happening the idle air control compensates for it by slowly closing. When the key turns off and the engine is restarted warm the IAC resets to the closed loop default position which is going to let more air in because the warm air is much less dense than cold so it needs a little more air. As soon as the computer realises the engine is getting too much air it adjusts the IAC till it smooths out. Regardless of what it is the reason the check engine light is going off because the vehicle goes through 3 successful drive cycles ithout having an issue. Which means the car is started and gets up to temp the computer goes into closed loop and then the car is shut off . It cools down and then is restarted and taken through this process again.
Wow so much indepth info and it all makes since guess my problem could be much bigger than i thought
Upstream sensors are the same, sometimes they have different part numbers but the only actual difference is the length of the wires/pigtail on them. Same goes for the downstream. His upstream sensor will work on any 90s OBD 2 GM with a 3.1. Its a coin toss as to whether the up and downstream sensors are the same.
Would it also be a coin toss as to which sensor is the problem? If either
That's what the code is for bank 1 refers to the side of the engine with cylinder 1 and bank 2 refers to the other side. Sensor 1 refers to upstream and sensor 2 refers to downstream. Each sensor has its own code dedicated to it. A V8 like my buddies GMC Sierra with the 6.0 has true factory duals and 4 sensors. Upstream is the exhaust from the cat to the engine and downstream is after cat. In your case where there is only one upstream sensor its labeled as bank 1 and when a car has 2 upstream and 1 down the down stream will always be labeled as bank 1.
P0171 is my code so thats bank 1 upstream correct?
All obd 2 codes are universal and if Andrew says 171 is bank 1 sensor 1 lean, I trust him. So yes upstream
The code bounces between Bank 1 sensor 1 lean, and System lean. Both mean the same thing I just think that the "system lean" is based on only having 1 sensor becasue that one sensor is the basis on the entire system. The upstream is the one or ones that influence how the engine runs. The downstream simply detects how well the cat is working. If the downstream fails it simply throws a code and the drivability of the car is uneffected. The sensors could be the same since they work the same way. However i usually see seperate upstream and downstream sensors.
Hey,,.. I have a 1995 pontiac Granprix..... it started about 2 months ago.. service engine light came on for about 5 minutes and then hasn't came back on since yesterday.....but was only on for again 5 minutes.......here's what its doing,.......my car starts up fine in the morning and goes....later in the day after its been drove....ill go to start it..it starts right up,but starts to rough idle like it wants to die out..ill give it gas (like rev it like a race car) then its fine..... it only does it at the end of the day after its been drove and warm....any ideas???
All i know is what Andrew and John have posted above
Check your fuel pressure and fuel pressure leak down
Well i replaced the upstream o2sensor last night and it didnt fix the problem i havent had the code cleared yet but that shouldnt matter should it? What should i do now?
The code won't go away for 3-5 drive cycles.
Any other sensors that would cause it to read "system lean"?
Maybe the system is actually lean. What did the old sensor look like? Black soot or ashy?
Lean... black soot would be the system thinking its lean and adding fuel, causing a rich mix. The extra fuel would then turn to carbon. The ashy white would be the system running lean and causing the exhaust gases to be very hot. Have you checked for vacuum leaks like Andrew mentioned before?
Ive checked all the hoses but still havent had someone put it on a machine isnt that what you mean or is there another way to check that im unaware of?
A vacuum gauge.
I have almost the same problem.. Car idles bad, slow reving somtime stalls . Keeps coming up with crankshaft performance range problem, egr. and exhaust is really hot. I replaced the front crank sensor and the one in the rear of the block to no avail. Do these have to be relearned ? with scan tool ? Cleaned the egr and it does not code anymore. did all the tests to the wires that run the crank sensor and cam sensor and they all test fine. Most testing points to the ECM any ideas?? P.S. all new plugs / wires/ coils. ALan
No they don't have to be relearned. Hot exhaust is again a lean issue and if your engine is running as bad as you say I would suggest running a fuel pressure test. Low fuel pressure would cover all your symptoms. A vacuum leak generally disappears with higher rpms and low fuel pressure gets worse with higher rpms. Have you replaced the fuel filter? If so how clogged was it? If you haven't it's less than $10 if you do it yourself..... If you start up a new question of your own there will be plenty more people seeing it and I would recommend listing more details on the symptoms and exactly what work has been done since your issue started.
I'm also a little confused about the two separate crank sensors.
I did a fuel pressure test and its getting 45 or so at idle, disconnect the fuel regulator and th epressure rises 10 ir so lbs. The pressure seems to pulse 45-40 though. fuel filter is clean. On the 3.1 there are 2 crank sensors I am pretty sure, the 24x and 5x one being behind the crank pully and the other that is hard to replace on the firewall side of the block , DTC code p0336 cranksensor range performance. Found one coil leaking spark, changed all of them.wires and plugs. When I clear the dtc and run the engine, it revs but labors a bit , them if I hold the throttle it will rev, then start to slow and surge a bit. once the code sets. the idle gets really bad. I ave heard these 3.1's have injector issues. But I dont want to change them out of there is something else bad. How about clogged partially , the catalitic converter ? In checking with a scan tool the 02 numbers on steady throttle above idle don't stay constant , or should they ? Lost, need help.
No the upstream should bounce -.5+ rapidly, does the exhaust feel like its a normal puff puff puff or is it just a steady hot stream? Could be a clogged cat. Yes the 3.1 are kinda known for their injectors and if you have an ohm meter you can test them at the control module without pulling the upper intake using a wiring diagram. The downstream is bouncing between distant numbers or staying close? If you have easy access to the upstream sensor pulling it would relieve the exhaust back pressure and allow it to run a little better, if a clogged cat was the case. What year is your car, I'll try to pull a diagnostic tree and put it on here, if you haven't already run through one.
Exhaust is Puf Puf , kida sputters during accelleration. Had the plenum off and injectors all ohm out ok. Not sure if they are flowing or not. Have to look at the dlownstream o2 which sould be sensor? ___ I will pull the upstream sensor and give it a try. The car is a 1995 model. 3.1 v6 . Appreciate all the help. Al
I don't know if the 95 and older all had the downstream if it did it will be bank 1 sensor 2 on the scanner its B1S2. I'll find some diagnostic trees in a little bit and post them on here.
The main thing I'm picking up is that the engine running out of fuel can cause this. give me an e-mail i can send this pdf to.
Try taking 1 of the coil packs off and checking for spec's. 12-14 ohms. Buy 1 new coil for $26. and start off replacing just one. Then see what happens. If that doesn't do it, then switch the new one to a different old one one the ignition module. Keep doing that and see if that makes any difference. Also, do an ohms check on the cranksensor. If you have a 7x its 500-900; 24x is 9.5 to 10.
Listen man. Go to the parts store and buy the intake manifold gasket for your 3100. Aluminum intake. That will solve your problem. That is where your leak is. Also..for shits and giggles pull that etc harness out and clean the years or dex crap off. ............mysterious gm tech
I just put an intake gasket on it last year
Check Engine = bad oxygen sensor. Last time I encountered this, the sensor was a stub, with none of the platinum still in place! Pull and inspect.
As John instructed i already replaced the o2sensors that didnt do anything
choked EGR? your smog mechanic inspect this?
The EGR in effect makes the car smell it's own farts (in a sense) if this valve sticks open it will only be breathing exhaust and not running properly.
Ok ill go find a smog mechanic thanks
simple part, you probably could fix it yourself. Pull and inspect yourself (you'll have to look at what this looks like on your car) but it's on the exhaust system and has a vacuum line to it. A mechanical flapper that diverts the exhaust back into the intake. It shouldn't be hard to find.
Ok thank you very much ill have to check that out i appreciate it!
Aftermarket intake manifold gasket probably by fel pro is leaking
any resolution? I've got a very similar problem with my 1995 pontiac 3.8 V6. starts fine cold, but once it is fully up to operating temperature, it will start fine within the first 15 min, but from 15 min ~ 45 min it will crank but not start. I've replaced many parts (IAC, Upper and lower manifold gaskets, plugs, ICM, coil packs, FPR)
Im at my wits end with mine as much as i hate too im going to have to take it somewhere
The only thing that I have been able to determine is that it "might" be the upstream oxygen sensor. Not sure. And it used to not do it in cold weather, however, that has changed this year. Plus, I was involved in a "minor" crash in a parking lot with an uninsured (at fault) driver. The damage will total the vehicle! So, I'm screwed! The basic front end is shifter to the right (left when viewing) pic.
Yeah i was told that also 75 dollar 02 sensor for nothing it didnt change a thing
O2 sensors thrown codes when reading abnormally. It has codes for being lean, rich, and broken. 96 and newer will idle rough and may die while trying to idle due to an O2 code because a bad sensor will cause the vehicle to run in open loop mode. Symptoms are number 1 and a guarantee check engine light on, 2 MPG decrease significantly, 3 possibility of a much cooler running engine because of the excessive fuel consumption and 4 is a rough idle when warmed up with the possibility of the engine shutting off. There are other symptoms but much less likely and pushing on the gas pedal will allow the engine to start normally. Pull the codes and go from there.
Been done over and over John. The code comes bas as a 171 which is VERY vague. My MPG has not/never had any significant dropping. The only thing that has been a positive noticeable difference is that I can most of the time get it to running up to par most of the time when acts up. However, I do not risk trips!
And what was the vacuum reading that needed to checked, my dads jimmy was idling rough due to a rotted vacuum line that fell off. Once the engine gets up to temp it goes into closed loop mode consuming less fuel which would make it run lean and maybe not start when in closed loop. It sounds like a vacuum issue is still on the table.
John and Nater my husbands car is doing the same thing. Above has been a very interesting read. My husband has replaced spark plugs and wires, fuel filter, cam shaft sensor and crank sensor. It has a new EGR value. He took it to the shop and the mechanic thought it was the fuel pump. Even though my husband did not because it would crank and run but after running awhile it would cut off or not crank if turned off. So my husband left his car at the shop anyway for the fuel pump to be replace and the mechanic called back and said it was not the fuel pump. My husband left the shop with his car still not knowing what is wrong. I told him to check the vaccums as John said above. So that is what he is doing now. He is throwing the same code 171. He car is a 1997 Lumina. He was told it could be electrical. Is that possible and what would it be?
Has be replaced the O2 sensor?
John, no we have not changed the o2. He just got two coil packs because they were tested and two were bad. I'll let you know how this turns out. To the other guy your mass airflow will not cause your car to not start.
P0171 is bank one lean not a mass air flow sensor. A bad mass air flow sensor will trip P0100 101 102 103 and 104. Mass air flow has nothing to do with the egr. Egr is based on the MAP sensor if its electronic or just the vacuum hose going to it. The engine running lean because of too much air or not enough fuel causes a P0171 and those both will cause a no start.
Everyone seems to overlook the fact that the engine has to breathe. If the Catalytic converter is old, it could block the exhaust when it heats up or it could be blocked. If the engine starts at all, it will spit and sputter and have no power because it cannot breathe. If your converter is bolted on, loosen the engine side bolts. You will know if that works. If it is welded in which most will be, I would spend the money and have a muffler guy cut it and replace it if necessary.
trprbob, the catalytic converter was replaced and the problem still exists. All theories lead to the two o2 sensors being bad. One suggestion was to clean them first with a carb cleaner to see if that helps any. If so, then it would be advised to replace them.
trprbob, the catalytic converter has been replaced with the same results. All theories lead to the two o2 sensors being bad. It was suggested that I try cleaning them first with a carb cleaner to see if that helps any. If so, it would be advised to replace them.
Checking for a vacuum leak around the intake is fairly simple. Grab a can of carb cleaner and lightly squirt it around the edges of the intake while the car idles. If it speeds up, you've found your leak... Be careful not to start a fire...
Using that method, I found my vacuum leaks. The boot for the PCV valve was split as well as the hose had pulled out of the connector on the back side of the engine. Once repaired, it still did the same thing for about ten minutes, then started running fine. Just like several have posted, do NOT ignore the possibility of a vacuum leak. When cold, it ran perfectly, once it attained operating temp, it would stumble, backfire and stall. Felt just like it was losing spark....
the 91 lumina 3.1 only has one ---one o2 sensor , there is no downstrream one on the 91---i hope that's the problem ,as mine has been doing the same thing for months and the car is now parked after all common sense and so-called diagnoses has been wrong and the experts said it could not be the o2...i am going to try a new o2 anyway in case it is ..good luck and wish me the same ..i myself have worked in automotive mechanics for 40 years and this problem on this car is the the darndest one i have ever seen ,, defying diagnoses from independants and 2 chevy garages alike. His problem , if like mine , means you have spark and fuel but when warmed up it flat out dies ...I do have a vacuum leak showing itself now so am going to track that down as well.
mine has done this same thing for months and i drive the other car now as 2 chevy garages and a number of independents have been wrong ...as have i a number of times and i have been a mechanic close to 40 years.if like mine-his has spark and gas ..but when warmed up is dead in the water .period.--The garages all said an o2 sensor will not cause this but i think it just may and if it does , the olde one is getting ..well that will be their problem then lol..anyhow--i do have a vacuum leak tieing in to the heater controls showing itself now so i am going to track that down as well...by the way -the 91 lumina 3.1 has NO downstream o2 sensor ..it only uses one ..one. Good luck to the original poster and say a prayer for mine . I felt likje a damned idiot , other than the gm call ion show and the chevey garages and the best mechanics in the tri-state area trhat I know have been as dumbfounded as me on this one as every issue that it should have been in order of cost and likelihood has been....wrong. And at this point their being wrong as to it not being an o2 sensor problem would not surprise me
by the way i realize his is the 96 , so it may have a downstream sensor - off top of headf it likely does , but not sure.---
So all these helpful posts over the last two years, and no confirmed solutions? Daryl/OP, any luck? John/Andrew, thanks for the hard work!
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