JamesDean

'95 Z28 M6, stock except for air intake and exhaust. New plugs (done myself ), new map sensor, tps tested good, iac in question, maf LOOKS fine (clean), all vacuum lines I can find good, and never a SES light since I've owned it, and no stored codes.

PROBLEM: When completely cold, I can start the car and drive 5 miles or 100 MILES, and car runs perfect the whole time. But if I shut it off and let it set for say anything over 10-15 minutes then restart, the idle is erratic usually goes back and forth from 500-900 rpm or almost dies, if I rev it, it feels like it's missing. If I keep revving it or drive it, it continues but I can get it to come out of it and then it runs perfect again til I shut it off. O2's possibly? (2 O2's, single cat car) But don't 02's trip an SES light?

Thanks guys...this is driving me crazy especially with no SES to help diagnose.

RE AND CHERYL

It's not the O2 sensors because the engine runs in open loop for the first 30 seconds or so even if the engine is warm. Only thing I can think of is heat causing the IAC to stick. You said you replace the Map sensor, are you sure? 95s don't have one. Do you mean mass airflow sensor?

96ZRDR

All LT1's have a map sensor regardless of year. How did you test your IAC sensor?

JamesDean

No MAP sensor? Hmmm...definitely has one...I replaced it a week ago when I did plugs. I hooked it up to vacuum and a meter on the bench and it read no voltage change with change in vacuum, so I replaced it. I agree with your 02 idea though...I knew about open loop, but don't know everything about 02's

JamesDean

did not test the IAC yet....took it out and carefully cleaned it, but didn't know how to test it at the time...how do you?

DrewHMS97SS

if the car was missing you would ge the SES light. it will blink the number of cyl is missing.

JamesDean

hmmm...yeah that's what I thought, but that was the only way I could describe how it was running...maybe it's not missing, just almost dying or something. either way this is driving me nuts....why am I getting no codes or SES light??? makes no sense to me...it has to be a sensor intermittently crapping out because it runs perfect in between these times I described....I'm thinking opti or anything major like that or egr or something would make it run this way ALL the time (and set codes/SES). More ideas?

Anyone, anyone?

TobyZ28

I dont think OBD1 will cause an SES (ie 95). OBDII might though (ie 96+).

Mechanic missed a plug on my car and it was running on 7. Didnt trigger any codes but i felt it for sure

JamesDean

My 95 is obdII...I think in 95 some were 1 and some were 2. And believe me, I can tell you I got EVERY plug!...including #8 without removing anything....that was an 8-beer-job, 1 for each plug, but plug #8 deserved 2 beers!

JamesDean

oh and this problem existed before I did plugs too.....also it's too intermittent for it to be plugs...has to be a sensor IMO

TobyZ28

LOL
I don't belive any 95's came from the factory with OBDII, even the Cali ones. The Cali's came with 2 cats but still with OBDI (There was another guy with a 2 cat 95 Cali Z and it is defiatly OBDI). My 95 is OBDI For sure too, single cat. I use freescan on it. They ALL have the OBDII Connector though....
Maybe yours is an OBDII But i'm not sure how to check for it. How many O2's do you have? I think OBDII cars have 4 O2's where the OBDI's have 2.... Also do you have 2 cats or 1?

OOps - back to your question though. I don't think you missed a plug, I was kinda just giving an example for the computer and my 95 not throwing a code My guess is your IAC passages may be dirty and/or the pintle may need to be replaced. Does the car go really lopey when this happens? Or just idles really weird until it comes out of it?

JamesDean

Well I've got 1 cat, and 2 O2's. I also have an old sunpro scan tool I use for my 94 Blazer and I tried it on the Z but it's definitely an obdII connector....guy at autozone scanned it with an actron scanner and it said no codes found. so what is it?? II or I?? and why a II connector if it's still I???

JamesDean

I took off the intake hose and cleaned inside the intake and cleaned through the top of the IAC port and when it was out I cleaned through the bottom of it, so everything's cool there...I just found a page on autozone explaining the test procedure for the IAC...I'm going to go down to the garage in a minute and check that.

TobyZ28

Why a II connector when its a I computer? NO IDEA. But thats the way the 95's are
It sounds like you have an OBDI computer. My 95, and ALL the 95's i know are the same way. Weird huh?

JamesDean

Well...IAC checks out fine....I tested resistance and it had 51-52 ohms between each pin it should....spec is between 40 and 80 ohms...keep the ideas coming!!