miss cookie

95 Formula LT1. 94,000 miles. No codes show up, service engine soon light not on. No stored codes. New distriputor, new plugs, new wires. EGR checked and working. Have 2 ECMs, codes don't show up on either one them, problem not effected on either one. Start up cold, nice idle, after a min of driving, rough idle, a few more mins driving gets worse. Sometimes shut off, start back up, nice idle, then gets rough again. New air cleaner, not the fuel, new fuel filter, fuel pump ok, has full power, no stalling, no backfiring, idle air vavles replaced, no vacuum leaks. Then there are times she'll be at an idle, rough, then smooth out for a while, then rough again. I have the book, but it doesn't say anything an on then off problem.

VoyagerCamaro

Around what temperature does it run bad? The factory LT1 PCM programming retards the timing when the water temperature gets hotter, cause they're is a higher chance of detonation (spark knock). Also two much EGR flow can cause the car to idle rough or surge when cruising. You could also try cleaning your MAF with MAF cleaner spray.

EDIT:What new opti spark did you install? Accel, MSD, GM, etc..

hrcslam

Sounds closed loop related. Check O2s and MAF. Exhaust leak?

miss cookie

The temp when the rough idle starts is her normal range, 180, or the quarter mark in the dash before 210. I don't know who makes the new distriputor since I had it put in
and she was doing this before the new distriputor. There is an exhaust leak. On both sides from her headers. I put in a new gasket on one side and that helped a lot, the other side has to be done and the shop that did it says the headers are warped. I can hear the other side leaking, but not the side that got the new gasket. Its doesn't seem like that side leaks at all after shes warmed up with the new gasket. So thanks, the MAF sensor is something I can do, and while at how about the IAC vavle? Clean that too?

miss cookie

There is a exhaust leak, at the headers. I had one gasket replaced and the shop that did it said the headers are warped.

hrcslam

There's your problem. Header leaks pull air in, causing a false lean to the O2's. The O2's are only used in Closed Loop (which occurs once the car reaches operating temps AND a certain amount of time). So it acts up a little while after a cold start, but sooner after a warm start right?

The false lean makes the PCM add fuel to correct, that will lead to a rich stumble.

Fix that leak, I'm sure it will fix your issue. Or, if you can, tune out closed loop.

miss cookie

Thanks, not what I wanted to hear. Yes, at times being off idile rough, start up is smooth for a few sec. then rough. Tell me how to tune out the closed loop, and do you know which headers to get that won't warp? These headers are 20 years old, I had them put on when right after I bought her. But please tell me how to tune out that loop till I get new headers.

hrcslam

You'll need a tuning program (TunerCats or TunerPro which requires WinFlash), a 16 pin ALDL OBDI Cable, and a laptop. If you haven't tuned before, it's not recommended to dive right into it. You'll need to do a LOT of research. A Lot! You need to understand exactly how the engine works (dynamically) and how each sensor factors into managing and adjusting it.

It'll likely be easier and cheaper to fix the leaking gasket. If they are warped, you could try doubling up the gaskets, but that's a temporary fix that wont last too long if it does work.

Basically any headers you get to replace those old ones will be better than what you have. The cheaper brands will have their own issues (my pacesetters needed some bolt holes pulled to bolt up), sometimes they don't though. The more you pay the better they'll fit right in without issue.

Your other option is to remove your current headers and see if they can be straightened. If so, have that done and be merry!

miss cookie

Ok thanks. If I decided to close loop, I would have that done. I agree new headers. This really helps me out, I can stop checking things and wondering what is her problem.

hrcslam

You can force open loop by disconnecting O2 sensors. If that solves your problems you know it's the exhaust leak for sure. It's a temporary solution though and it will trip your check engine light.

SS RRR

iTrader: (2)

How old are the O2's?

miss cookie

I was thinking about doing that but didn't know the results so thanks. The check engine light is now coming on for the first time and I don't have a code reader for her, obd 1. I have tested the maf and egr by the book and both are ok so screwing around with them might be what set off the light. So I'll have to seen if I knocked off a vac hose. Thanks again.

SS RRR

iTrader: (2)

?
If your O2's are old you can experience issues like you've described. Sometimes there have been posts of those stating there has been no SES light.
As stated, unplug your O2's and get to normal operating temp to see what happens.