Ok, here we go. 94 Z28 auto with the old style computer. Runs fine for about a half hour to an hour or so, then starts acting up. In gear it will start to idle rough and the IAC will open all the way to 160 and the idle jumps up to about 1200 RPM's, still stumbling. When put back into either park or neutral it will rev up to about 2000 RPM's until the IAC has a chance to close. Then it will idle ok. Once in a while it will rev up a few hundred R's even in park or neutral. When driving, cruises fine, but when jumping on the throttle about half way it falls on its face and stumbles bad until I either let off or go WOT. At WOT it will downshift and take off, but kinda stumbly. Not too bad, but noticeable. No check engine light. No codes. Nothing is out of spec when put on a scanner. When IAC is disabled at idle it stumbles all over. It won't idle up cause the IAC is disabled, so it just stumbles. It does not stall. I'm sure it's not the IAC. Something is telling the IAC to open, and no one can't figure out what. Again, no codes or lights and it check out fine on the scanner. The guy who I had scan it owns a shop who mostly deals with 3rd gen camaros, so he knows his stuff, but I still stumped him. We were gonna swap out the computer just to see if maybe that's what it is. Anyone have any ideas???

 

TTT Anyone???

 

If you have a extra computer try that, I had a PCM go bad once.. I had similar problems in my Formula except mine would die unless I kept the RPMs up.. It would stumble real bad. You might check your ICM I replaced mine and it fixed it.. My car ran great in the winter but once the AZ heat got to it I think the ICM was overheating killing it.. The next summer it did it again, I gave up and bought a 94 Z28. I was convinced my Formula was cursed, I think I replaced every sensor on that thing...

 

Please explain the following:
1) In your signature it says "Holly Intake"
2) Do you have an EGR?
3) Have you thoroughly checked the TPS?
4) What does old style computer mean? 93?
5) What is your vacuum level before and during the problem?

 

1) Sorry, I meant Holley. Typo.
2) Yes, there is an EGR and it is operating normally.
3) TPS reads .4V with throttle closed and 4.7V at WOT. All is normal.
4) It is still a 94 computer. I guess there are 2 types though. The older one you can't do self diagnostic from the check engine light. The newer one you can. Also, the older one doesn't show as many things on the scanner as with the newer style computer. The guy I had scan it said he knew there was a such thing as an older computer in the 94's, he had just never seen one before mine.
5) Vacuum level is normal according to the MAP sensor. I would have checked it with my vacuum gauge but I'm still waiting for it from the SnapOn guy. (I bought a tool set and I got a broken one.)

 

1994 computers in the LT1 f-body are all the same (same as a 1995, too). 1993 computers are different and you can still flash the codes with the SES. 1994 and up you cannot.

If the IAC is actually working properly, I would be sure you had no vacuum leaks and perhaps any leaking injectors.

 

The reason I asked the question about the Holley intake was, we call the breather CAI. Not intake. I assumed you changed the "INTAKE" to carbureted. Now that you changed the signature to FIPK, I understand.

If the Holley uses a cotton filter, did you oil it? Did oil get on the MAF? Did you pull the screen out? All this adds up to NG. Have you tested it by disconnecting the MAF? Have you cleaned it?

 

well, there is a "Rev B" which is somewhat different as far as programming goes.

 

Sounds like an opti problem to me. It could be a PCM issue but I would suspect the opti. If you have access to a GM tech2 scan it with that and watch the low and high resolution signals.

 

Where is this information from? The stored programming can change as updates are available. That does not change the physical PCM.

 

as far as I know their phyiscally the same, when i ordered my Tunercat definition file he sent me two, one was a standard EE file common for most 94-95 PCMs, the other was a EEB file, which he explained that a few 94 PCMs were coded differently and needed a different def file to read them correctly, he said if you use the wrong one you would get some very strange readings.

 

Sorry about the confusion. And yes, it is a cotton filter although that's not the problem. The MAF is descreened, but it's still not the problem because I tried disconnecting the MAF and the problem still exists.

If the opti was the problem wouldn't it at least throw a code for a misfire??? Even if it's not the opti, I just don't understand why it's not throwing a code.

By the way, today I had my Fuel Systems professor take a look at it for me. Hooked it up to another scanner and found no problems again... That's two knowledgeable people I have showed it to who I have stumped. He said on Wednesday he's gonna make a lab for our class on how to set the minimum idle air screw. He said the cover was off mine and someone might have messed with it. We're gonna set it to the right setting just so we know it's correct.

Also, today I replaced that flat gasket on top of the TB. I was kind of curious as to what was under that cover, so I took it off and noticed the old one looked like it was getting sucked down and getting stretched out. It had a large dip on the left half of it. I was thinking MAYBE it was getting sucked down and blocking the port off. I don't know, but I figured it wasn't good, so I replaced it but have not driven it yet to see if it fixed it. I'm getting desperate now.

 

everyone was telling me my high rpm miss had to be the opti, ended up being....well im not sure what it was lol, but i converted to OBD1 got new O2s, and knock sensor and it went a way . But anyway, my point is there is a lot of things that can cause misfires and such besides the opti.

 

Ok, well sence everyone likes to just jump to the opti I'll consider it. But, there must be a way to test it. There is a way to test everything, and at $250, im gonna test it before I just decide to throw one in. Anyone know???

 

It wasnt as much the 250 for me, as the labor to put it in (considering I didnt know how to put it in)