My '96 LT1 that I just got has a rough idle after it warms up. Reminds me of dirty fuel injectors (from past cars)....as you can feel it in the car and watch the RPM's go up and down (very little 50 rpm or so).

It also has a hesitation when punching it from a standstill and when you run it to redline (WOT). I don't want to call it a miss as it just feels like somethings holding it back.

I changed the plugs with AC Delco Platinum replacements and fixed a large VAC leak on the PVC Valve Hose. These seemed to help but the problem is still there.

When the car is cold the idle seems fine (though it is a tad bit higher when cold).

Any ideas? Car did sit for over a year and the guy I got it from put it on the road back in June. He didn't drive it much and then I bought it.

 

I am getting the same symptoms as you. I have detected my miss to be a fuel pump on it's way out.

 

Driving around with vacuum leak you probably killed your O2's by running too rich.

 

Well the miss/hesitation is still present at WOT. I am getting no service engine light. So therefore I am assuming that I do not have an O2 sensor problem.

I'm really suprised no one has chimed in and suggested the opti distributor. From what I've read it seems like I have the symptoms of an opti failure.

What does everyone think?

Is there a way to be pretty sure it is the opti before I replace it?

I just want to be fairly sure before I go and spend $300 and a whole day or more replacing it.

The car also seems like a dog off the line. If I try and smoke the tires it boggs down and then seems to go after I get past or around 1300 rpms. Same goes with trying to powerbrake it. The hesitation/miss comes at higher RPMS (>5000). At idle you can feel it miss when its warmed up (especially when in gear). Cold idle is fine.

 

I can also hear a very slight popping sound from the driver's side manifold area.

 

popping from drivers side manifold i dont know about, but i do know that the first symptom of an opti on its way out is a small hesitation/miss above 5k after the car is warm, so im guessing as it gets worse it would occur at idle too. mines just starting to hesitate a little at cruising.. so i dont have much longer left with my opti

oh wait, that popping is it sorta like a tick? i know theres a weld on the heat shield that likes to break loose (ive heard of a few others with it) mine just started that recently, only does it in reverse for a few seconds and when accelerating. thats how i know its not a rocker or at least im hoping..

 

Might be rotting O-rings on the injectors. If the car sat for over a year, could be a possibility.

 

As far as the miss while cruising. I get a miss or very slight buck or two or three when the torque converter is locked up in OD and I'm slight pressing the gas. I would say this goes away after a certain speed (say somewhere aorund 65-70mph)

 

really?? hmm maybe my opti isnt as far gone as i thought... oh well its still time to replace it, car is readin 148.6k and on the original opti far as i know =/ (94 non vented! )

 

Better to change it now instead of on the side of road at midnite!

 

yah i got the same problem the car runs perfect cold idle like 1000rpm a4 but once it warms it idles rough and if u give it quick snap with the trottle it was hesitate stumble i dunno just have a bad shake to it. But ive replaced


coil, wires, plugs tr55, o2 sensors cleaned maf, tps, and iac, deleted egr and air and after all this it still does it.


But it has to be some dumb sensor or something when the car is warmed up in closed loop. Cause i thought maybe it was idling to low still idles at like 600 but none the less.. So when the car was warm I held it at 1000 and snapped the trottle and it still shook, unlike when the car was first started it would roar or really pick up.