M G Brewer

I have searched and searched for a potential fix to my poor idling problems on my 1988 5.7 IROC. I bought the car with it running the way it is, so I don't know what all has been tampered with since before I purchased it.

The car runs perfect when you first start it up. After it warms up it starts idling so low it wants to die. It hardly dies, but when it does it seems to only happen at a stop light lol. If you gas it hard from take off it will die sometimes too. If you shut the car off and turn it back on, it runs perfect again for a few mins/secs.

I checked the codes and here's what I came up with:

12- Diagnostic mode / ECM functioning No reference pulses to ECM.

22- TPS (Throttle position sensor) voltage low OR Fuel cutoff relay
circuit open or shorted to ground.

33- MAP (Manifold Air Pressure) sensor voltage low – pressure low/vacuum
high OR MAF (Mass Air Flow) sensor signal low – flow high.

34- MAP (Manifold Air Pressure) sensor
voltage high – pressure high/vacuum low OR MAF (Mass Air Flow) signal
high – flow low.

36- MAF (Mass Air Flow) sensor
burn-off circuit failure OR fault in direct ignition system OR Missing
pulses in electronic spark timing signal.

45- Oxygen sensor rich error.

I am just needing some guidance on where to start spending the money. I was going to buy a new MAF, but don't want to spend $125 on something that might not be broken. I have replaced the IAC and TPS. They are both set correctly and the car runs just as it did before I replaced them both. Any help is appreciated!

Tuned Performance

iTrader: (92)

I wouldn't worry about the code 45. 33 & 34 could be throwing because of a bad ecm or maf.
The rich o2 is bacause your running in limp home mode.
You might want to try this test first.
http://chevythunder.com/tps_code_22.htm

M G Brewer

I'll give that a shot.

blacksunshine'91

iTrader: (10)

Just curious, when your HVAC controls are moved is there a hissing sound? If so, that vacuum leak can cause an idle issue. Here's a link for what I am talking about and an easy fix for the issue:

https://www.thirdgen.org/forums/inte...anent-fix.html

redneckjoe

couldnt hurt to verify correct ignition timing. i chased a similar problem on a TPI only to find that the PO never tightened the distributor bolt down.

M G Brewer

Put a brand new MAF in today and still runs like doodoo. I will keep pushing on!

M G Brewer

Wouldn't a vacuum leak cause it to run poorly from a cold start? The car runs like a champ when you first start it up. Once it warms up, it goes to crap.

zed-028

Vac leaks can stuff you up from the word go.

when you changed the sensor did you pull the + lead and reset the ECM?

M G Brewer

I didn't reset the ECM. I thought once the problem was fixed that the SES would go away.

M G Brewer

I was fooling around and kept adjusting the idle up until it smoothed out, then unplugged the MAF burn off relay and the car started idling up a lot, so I plugged it back in and lowered the idle back down to normal and it ran perfect. Shut the car off, fired it back up and it went back to crap again.

Tuned Performance

iTrader: (92)

The low idle running rough is most likely because your in limp home mode. You should diagnose the issue with a flow chart.
http://www.chevythunder.com/maf_code_34.htm
http://www.chevythunder.com/maf_code_33.htm
http://chevythunder.com/tps_code_22.htm
Once resolved you should reset the min air setting.
http://www.iroczone.com/2009/10/clea...rol-iac-valve/

zed-028

sometimes, but i would say 80% of the time no, it will stay

either pull the positive lead from the battery for a few minutes or disconnect the ECM from its plugs for a few mins.

that should reset the codes - if any of those conditions still exist after a run then those are the ones still plaguing you.

M G Brewer

Put a new MAF starter relay and MAF burn off relay on. Problem still exists, though now it is only flashing code 36.

M G Brewer

PROBLEM SOLVED: ECM OR CHIP WAS BAD.

I bought an ecm of a member on the board and all my problems went away. Hope this can help someone else. It sure has been a long depressing road, but now I can finally start to enjoy the car some.