John Hagan

Been having these idle issues on my 88 IROC since I've bought it, and today it stalled out while I was at a stop sign. My idle goes pretty low (between 500-1k) while stopped after the engine is warmed up, when traveling somewhere around 30MPH, the RPMs will fluctuate when I let off the gas (drops down to around 1k, then back up, vice versa).

I've replaced the IAC, that didn't work. I just replaced the 02 sensor last weekend (I got the NGK, I avoided Bosch), and that didn't work. I'm getting fault code 13, which points to the 02 sensor or TPS sticking or being misaligned, but I'm also wondering if it could be the EGR valve, because now I'm reading that they are a common problem. Also, I don't believe the TPS has much to do with the idle.

I probably won't be able to get much done this weekend with the big snow storm coming in, but I wanted to post here to see if I could get a more knowledgeable opinion.

Schurkey

Connect a REAL scan tool, look at the data stream. The answer is there.

For the record, just because the IAC is "OK" doesn't mean it's working. You could have corroded connections or a broken wire in the harness so the IAC doesn't function even if it's in perfect condition.

Same with the O2 sensor--the sensor may work beautifully, but if the wire harness is damaged, the input doesn't get to the computer.

Ron U.S.M.C.

Schurkey is right on the money, as usual.


If you don't have a scan tool at this moment this is something you can do.
There is a procedure within this thread that explains how to properly reset the IACV and Minimum idle speed.

It starts with setting the base timing to stock then goes from there.
= https://www.thirdgen.org/forums/tech...dle-speed.html

Ghettobird52

350 TBI, so it was swapped in at some point? If so, what was done with fueling and Computer?

John Hagan

Previous owner swapped out the 305 TPI for a 350 TBI for some reason. I'm not sure what was done with the fuel system, but I asked him and he did say it had the original ECM for the 305 in it.

John Hagan

I'm currently looking at a computer (1227747) from an 89 Chevy Suburban. 350 TBI, 700R4 just like my Camaro. Just wondering about compatibility issues, if any.

Ghettobird52

There's your problem. I had the EXACT same symptoms when I swapped from 305 TBI to 350 and left my 305 ECM in place. You should only need some tuning and a fuel pressure regulator because the TPI fuel pump will supply adequate pressure for the 350 TBI ( 305 TBI fuel pump will not)


Actually I don't think it was a TPI because the TPI ECM will NOt work with the TBI motor.

Ghettobird52

cant remember the exact differences but there are a few, i would recommend you to look into Rbob's EBL Flash. Greatest mod for your swap.

John Hagan

Unfortunately that's out of my budget, as I'm laid off at the moment. :\

I found the Suburban ECM for $35, I was really hoping it would be what I needed.

Ghettobird52

I understand that! I actually bought EBL Flash TWICE! Once 5 years ago, got laid off and sold it.... then about 2years ago i bought it again lol.

yeah a 350TBI ECM could techincally work but from what i remember the only ones that can swap with our ECMs are the "B-body" Caprices.

John Hagan

Thank you very much for your help! I'm sure I'll come across one soon, hopefully.

Ghettobird52

Dont quote me on that, I recommend you to send a PM (personal message) to Rbob. Hes a moderator here and also the creator of EBL. He will be able to tell you if that 7747 ECM will swap with yours or not. Hes a Nice guy, he might even chime in here if he sees this before you make it to a PM.

John Hagan

Sent him a message and he confirmed that all is good with that computer. So that's great, can't wait for it to come in the mail.

Ghettobird52

Sounds good!! Update the thread once the ECM is installed!