Rough Running


Asked by Oct 13, 2008 at 06:29 PM about the 1991 Nissan 300ZX 2 Dr Turbo Hatchback

Question type: Maintenance & Repair

ok so i have my 91 nissan 300zx turbo with 100,000 miles on it and im a nissan tech so i should be able to figure this out but im sumped anyways, so im wondering if anyone has any ideas? ok so my car has had this problem lastely where most of the time it idles really rough and even under normal driving it runs rough. usually the only time that it runs really well is under hard acceleration. i have replaced all the ignition coils, all the spark plugs, cleaned the whole intake and the fuel pressure regulators. i know i have a leak in my exhaust but i dont think it would make it run like its running and ive also checked for vacuum leaks but i cant find any. im thinking it might be a stuck egr but i cant even find it to fix it if thats what it is. just any ideas from anyone would be greatly apprectiated. thanks -devin

23 Answers


I'm not familiar with the 300z so I can't be much help at all, but I can think of a handful of things that would cause this... Have you run a compression and leak down test to ensure you don't have a bad cylinder or a burnt valve? The symptoms sound like the timing is off... As I said I'm not familiar with the vehicle so I don't know off hand if it's got a dizzy or a crank fire system so I dunno if the timing getting off is an issue with your car. Another possibility is one or more injectors are going bad or are dirty. If you've got time and another ride I'd send 'em off to or a similar service just for piece of mind... Assuming they are original, they are fairly old. Hmm... The exhaust leak shouldn't be an issue if it's minor and/or downstream of all sensors... If not it could result in a bad a/f ratio, normally that just results in lost power though... Sorry to say I've never worked on a 300z so I'm just thinking in general terms here. Wish I could be more help, keep us posted though m8.

2 people found this helpful.

Well to me it sounds like you are loosing compression on a cylinder. have you OHMed your injectors and done a compression test? Under hard acceleration you aren't going to notice it as much, because RPMs will be rotating too fast to notice. It also could be a misfire if RPMs steady drop, but with the coils and plugs you shouldn't have any problems. Cheapest way to figure this out, would be replace the fuel filter, OHM the injectors, compression test.

3 people found this helpful.

Back when I was a nissan tech, I ran into a similar problem with a few 300's. could scan it with the consult, and no codes, sure enough, I just unplugged the oxygen sensors, and took it for a drive, and usually the problem was fixed. installed a couple new o2's, and problem was fixed for sure.

9 people found this helpful.

i just got a tt its a 91 as well mine has began doing the same thing have u checked the timing on it??

2 people found this helpful.

i havent done the o2 change but whenever mine statrs acting up i always get on the expressway drive like at 85 90 for like 5 min and the problem seems to go away the think i do alot to help it out is put like 20w 50 oil the pressure soes rise a bit but like u said its an old car need to be better taken care of and do the oil changes every like 1500 - 2000 miles hope this helps i also heard that the 91 was the worst year for this car im looking to get like a 93 last year b4 the inspection restricons were added on


Did u check for error codes? It sounds like the same issues I had when the driverside o2 went out.

2 people found this helpful.

there are no codes


I would check several things.... The first would be timing. The second would be to elaborate on where you exhaust leak is. If your dumping exhaust before the turbo it could be causing the computer to put too much fuel into the cylinders. Next i would check the egr. Look in the factory service manual. It is a pain in the ass to change but everything with the TT Z's is a pain in the ass. Or it could be compressor surge, or it could be a stuck wastegate or lots of things...


on e last thing u should check its a long shot but it might work sound like air/fuel mixture isnt right check the connection on the MAF and tighten the connection clips on the harness that doesnt come out on the error codes if not it woulsd probably b the timing

1 people found this helpful.

I just bought a 1992....same problem....have the dealer check the "POWER TRANSISTOR UNIT". it was a recall on all the 1990-1996 300zx's... Let me know how it

4 people found this helpful.

Injectors are a big issue for the 90-93. The biggest thing with these cars are not a lot of places know how to work on them due to the small engine bay and rarity.

1 people found this helpful.

Try a power balance test, turning off injectors one at a time while its running. When you shut one off and the idle doesn't change, that's your misfiring cyl. Check the resistance on your injector. I should be 14ohms. Any higher, and it's bad. Buy and install all 6. If you don't, others will die soon, trust me.

7 people found this helpful.
Best Answer Mark helpful

I've cleaned the connector to the coolant temp sensor ant the mass air flow sensor. It seems to be running betting. I know all my cylinders are firing but Its still running rough at low rpms and running really rich. I can smell the gas. Since its steadily getting worse I believe it to be the o2 sensors. I am having my mechanic do a diagnostic for me to be safe before spending 120 dollars on o2 sensors if they are not the cause. He is the only one I know that has a one piece connector to run a full diagnostic test and will report back and let you know what the cause of this is. I highly believe its the sensors at this point.

1 people found this helpful.

Odds are with an older z like that your problem lies either with a faulty injector, or corrosion on the terminals on most of the connections. First thing i would check is to unplug all the connectors from the inectors and do a continuity check across the terminals on the injectors themselves. should be between 10 and 14 ohms. Matco makes a great terminal cleaning tool for the connectors, they are like little diamond tipped tweezers to clean the pins off both sides. main connectors to check are the tps, cas, injectors, iacv, knock, and mafs. If your egr is stuck, you'd have to either pull the plenum or the trans to access it.


It ended up being the injectors


When my 90 300zx TT is cold it runs perfect. But once it gets all warmed up thats when the problems start. It runs fine and boosts fine but the problem happens when i go to stop at a light or stop sign. The RPMs drop below normal and the car almost dies and then once i fully stop or am about to the go back up. A few times they drop so low it dies on me. Im confused on what this could be. Ive cleaned out the Idle Air and also re set my Idle to factory. Cleaned all sensors and my air filter. And im running on all 6 cyl. I need help with this and ideas it could be.

3 people found this helpful.

Check the ptu my car is doing the same thing it idles at 900 and jumps to 1200 misfires under normal load and acceleration and clears up under hard acceleration one day my friend drove the car and the car died and it wont restart at all and premier z says it is the ptu

3 people found this helpful.

Can some one help me with my 93 nissan 300zx twin turbo plissss


I brouth this car like a 2 months ago like its ok .. this is my problem well not mine this fucken car is driving me crazyyyyy is manual ok when I star its like shacking a little but when I put 1 gear run good but when im bout change gear like its cut off like the pressure or gas dat happend everytime I change gear I can aceelarate to much becaused its like lossing pressure.. wat I have done......I have change the fuel filter.fuel pump.i check for pressure on the motor is good injector mechanic check n he said is good...I removed the cataly conveter same problem..I change the computer same problem well got worths when I change the computer.. shut down everytime I get to a stop ...can some one help meeee plissss

1 people found this helpful.

the EGR valve is located on the back side of your motor, there two 3/8 tubes running around both sides of your valve covers, follow them to where they meet in the middle, and thats where you'll fine you EGR valve replace it. And while your back there change the AIR SENSORS. There on the exhaust pipes strait down from the two tubes, I talked about earlier....hope this helps


Devin here's a picture that mite help

3 people found this helpful.

Dude check the inside of the connectors on injectors you'll find green death corrosion on each connector, buy some ev-1 connectors clean injector terminals and replace cylinder head temp sensor and sub harness still avail through your dealership. Hope that helps.

My ignition timming won't stay at 15degreese tdc what could cause this iv put a new timming belt on car will crank and run but idles rough

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