driving issues

50

Asked by Jun 14, 2010 at 04:23 AM about the 1988 GMC Suburban

Question type: Maintenance & Repair

my year wasn't available in the selection, I have a 1988 Sub that has some acceleration issues.  More specifically, driving in general.  On initial startup, the beast runs fine, no misses, no rough idle, just perfect.  A minute or so in, the rpm's lower as if it were to stall and the idle is rough like it is missing a cylinder.  It runs excessively rich also.  When i put it in gear, back up out of the drive and start to roll forward, it acts as if it is flooded and I have to push accelerator pedal to the floor to get moving.  once moving and cruising (at any speed) all is well.  No missing, flooding or loss of power, although it still runs rich.  If I were to accelerate to speed up, there is cutting out, sputtering, acting as if it is flooding out and lack of power.  If I floor it, about 10 seonds or so later the engine clears out and power is restored with no missing or cutting out.  I have replaced the temp switch on the intake that sends the signal to the ecm.  I have read the wires on the tps and checks good.  I put vaccum on the map sensor and found it bad and replaced it.  The throttle body and distributor is good.  Can someone please help.  I am going crazy trying to fix it.

15 Answers

9,395

Take your EGR and inspect it for excess carbon buildup and ensure it is not stuck open. Also, check for any broken or cracked vacuum lines. Is yours CARB or EFI?

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50

sorry to mention that the EGR was replaced, the old was sticking. I believe i have checked all vaccum lines. I replaced most rubber near the intake and heat sources as some of them were dry rotting. I checked the joints between the hard vaccum lines and rubber connectors. A friend had said that the temp swith on the intake that sends the signal to ecm could be out of calibration. If the coolant temp on the switch is a few degrees cooler than what the ecm is reading then the ecm would automatically adjust the fuel air mixture to run rich thinking it is cold, essencially "choking" the system. what do you think??? Did i make any sense of that?

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50

by the way, "375" the post to myself is supposed to be back to you as well as this one. the vehicle is TBI. I am at the point to tear out the intake and tbi and revert back to carburator.

9,395

Although possible, it would have to read a lot colder for it to even become a possibility. It is more likely that you have an injector sticking open or leaking. Maybe even a faulty fuel pressure regulator.

50

I had replaced the TBI which eliminates the injectors. As for the pressure regulator, isn't that on the TBI as well??

9,395

No, GM usually mounts it to the back of the cylinder head. Just back-track the fuel line. Check to make sure the vacuum line coming off of the regulator is not cracked or broken. For that matter, check to make sure no vacuum lines are. The regulator operates off of engine vacuum.

50

I will check that out today and let you know what i have found. thanks.

15

on the 88 to 92 4.3, 5.0 and 5.7 liter there is an idle air control motor (IAC) it has a square plug with 4 wires if the valve is stuck it will produce alot if not all of your symptoms. try replacing that. also when its been running for a while look under the truck and check the exhaust. see if its red hot. the cats may be plugged.

9,395

A bad IAC will almost always cause a "searching idle," I have never seen one create a "flooding" effect... Now I do agree with you on the possibility of a clogged cat.. It would create the symptoms.

50

I will check the IAC and replace it to eliminate the part out of the loop. Between you me and the fence post, there are not any cats on the vehicle. I took them off about 8 years ago. Thanks for the input, i appreciate it.

50

hey there, sorry it has taken a little while to get back to you, it has been unbaribly hot here in the Carolinas'. Anyway, the IAC suggestion makes some sense but when i put the new TBI on it had a new IAC on it and it still ran the same way. as for the suggestion of the fuel pressure regulator, there is not one between the heads and firewall. i have traced the fuel lines all the way back to the tank and there isn't anything that resembles a pressure regulator. unless it is inside the tank with the pump, then that is another ball of wax i was hoping to avoid. I am at my witts end and ready to convert it to a carburator, at least those i can rebuild myself with confidence. Any other suggestions could make a difference. I am currently saving the money for the conversion so there is a little time to tinker with it as is (about 4-6 weeks). Thanks in advance and hope to here from you again soon.

15

did you disconnect the battery negative for a few minutes to reset the ecm ?

1 out of 1 people think this is helpful.
15

this is incorrect in an 88 the fuel pressure regulator is in the tbi unit.

35

i just signed onto this forum because i have the same problem with my 88 2wd 1/2 ton suburban tbi 350. i replaced egr and iac, fuel pump, fuel filter, and fuel pump relay have all been replaced. but engine still stalls,if i keep revs up will search for idle then stall if put in gear or let off revs for to long. i was thinking it was a vacum leak, but i really am not for sure. did you ever solve this problem with tbi or did you convert to carb?

1 out of 1 people think this is helpful.

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