I have an 86 IROC that I’ve been having a few issues with. One morning I was driving down to work as I normally do and noticed the car started idling pretty low out of nowhere. When I put it in reverse, it shut off on me and gave me some trouble to start back up. Eventually got it started but it was still idling pretty low, my tach doesn’t work so can’t give an RPM unfortunately. Ever since then while sitting in traffic it’ll randomly change idle speeds and start idling super low to the point where it wants to turn off, it’ll do this for short bursts and then find its way up to a normal idling speed. Any help? Also when I put the car in park, it’ll idle super high but adjusting the idle speed will make the car turn off whenever I put it in gear.

My father and I checked the distributor, swapped out a few pieces, got new spark plugs and spark plug wires just not sure where to go from here as the issue still remains. I’ve driven the car twice since this and it gives me no problems early mornings after I let the car warm up but it acts up in the afternoon when I drive back home from work. 5.0L TPI engine by the way

 

Sounds like either the IAC or the ECM has issues... I would start with the IAC and it's passages...

The ICM can also be at play here... If it's going, it can mess with timing... And that affects idle speed...

At least this is my experience....

 

Any codes or check engine light? I would take a look at the TPS/throttle position sensor or as erik mentioned the ICM which when they get hot can act up when they are on their way out. If you have a voltmeter I would check the voltage for the TPS to make sure its within spec. Jrobling on YT had a good video on testing it and lots of info on here too.

 

Cool, thank you for pointing me in the right direction. Will be doing some research and checking things out in the morning

 

So I ran through the codes that it was giving me. Codes 35 and 36 came up which if my research is correct, has to do with the MAF and the IAC? The car was missing the MAF entirely when I bought the car but it does have an IAC. I ordered new ones of each so hopefully before the end of the week I’ll have those installed. If the issues still continue, we still have the old ECM from my dad’s car that we can swap out if needed

 

Most likely related to MAF circuitry. They are a pain in the *** to diagnose. I am in the middle of it right now with my IROC-Z 89. I just changed the MAF for a Denso one and I will report later. The ECM started throwing code 34 once in a while and lately I've got a code 36.

https://www.thirdgen.org/forums/tech...t-ok-then.html

 

Just want to give you a heads-up. I am in the middle of installing a new MAF (Delphi #AF10320) on my 89 IROC-Z. The Delphi fits perfectly. HOWEVER, be aware that the "voltage scale" could be different from the original MAF GM used almost 40 years ago to calibrate the tune. Preliminary datalogging shows over rich condition at low air flow. This is due to the fact that the new MAF is offset by about 0.20V at low air flow. My car was running too rich and stumbling with new MAF. I am in the middle of retuning the MAF tables to fix all that. SO just be aware if you install your MAF and the car runs like s***, it could be the issue. At low air flow an error of +0.20 volts is significant.

 

Just wanna make a quick update to this;


finally got around to working on the car after about a week and a half of no progress. I purchased a Duralast MAF (part #DL-6014) as well as a Duralast IAC (part #AC102) from autozone. Installed both and the car seems to be running a whole lot different than before. I still think it might be too early to fully say that my problems were fixed but so far so good. I noticed the downshifts are a lot smoother, the car would sort of jerk and you could feel when it shifts down but now it shifts smoothly. Also seems like the fuel efficiency got better. I assume it’s because the car is properly gauging the air/fuel mix and it’s burning less gas because of it. SES light is still on, I’m sure it’ll go away with time but I doesn’t bother me much.


I’ll do a few more trips in the car before I say it’s fixed but I can say it’s running a whole better than it was. I really appreciate all of you for pointing me in the right direction, and getting my car running as it should!

 

What code is it throwing? SES light isn't supposed to be on.

 

Really? I read that disconnecting the negative terminal for a bit will erase the codes but I thought the SES light goes away on its own after some time. I will have to check what codes it’s throwing perhaps in the morning and will let you know

 

Depending on your .BIN, could be 50 cycle times without error before clearing. There should be an ECM fuse you can pull to clear code. Either in fuse box (10amp) or under hood near battery (20amp)