1994 850 Good Idle Cold, Stumble Warm

[Milkmanx]

Due to a bad RMS we decided to pull the motor and tranny. All went well and I decided I would perform the following while it was out.

Replaced
RMS
Oil pump and pick up seals
Main tranny seal and axle seals
S1 and lock up solenoid
Timing belt and several tensioners/pulleys

All went good putting it back in. Took my time reinstalling hoses and connectors and got it back together. Filled up fluids and cranked her up. I warmed the car up and it had a good idle. Topped off the coolant. At this point I have not hit the gas pedal at all, just let it idle. Once warmed up to the 3 o-clock position I tapped the pedal a little and it began to give rough idle. I continued to check hose lines, connections and anything I can think of and found nothing. Next day I cranked it up and it was a perfect idle. I let it warm up again to the 3 o-clock and tapped the gas and got rough idle.

Over the last few days I have replaced the temperature sensor and re-wired the wiring harness side for a better connection. We checked the fuel pressure and found it to be 40 which should be in spec. We did a compression test and found 4 cylinders to be about 180 and 1 at 155 ish. One important note is during the timing belt install I did ever so slightly turn the crank and tapped a valve. When it happened I I remember thinking it was really to light hit to do any damage so we moved on. Now with the low compression I have to wonder if it did do damage but I do think the hit was very very light. We hooked a compressor to the low cylinder looking for a leak in the exhaust and could not hear one in that cylinder.

The real question is why when the engine is cold I have an almost prefect idle but after it is warm it gets rough with a louder than normal popping in the catalytic convertor? Should I expect to see a slightly bent valve on the cylinder with low compression? Is there some other correlation between the cold and warm we should be looking in to? We did order the timing/valve cover kit, should be in next week to double check the timing.

Keep in mind the car was running very well prior to pulling the motor. I had done a ton of work, tune up, pvc system, cleaned EMF, and tons of other things. Never had an idle problem, just wanted to get new RMS before it started to get cold.
I will also add I did drive the car a little in its current state. The car drives very much like it did before and can hardly tell there is any problems when moving, only the rough idle and popping in the cat..

Thanks for any help you can provide.

[AVIP]

See I was assuming dirty or bad idle air control motor but with popping in the cat makes me wonder. Hopefully I read this right just skimmed a but but did you reset the computer after engine swap? (consists of removing battery and holding foot on the brake for half a minute)

[Milkmanx]

See I was assuming dirty or bad idle air control motor but with popping in the cat makes me wonder. Hopefully I read this right just skimmed a but but did you reset the computer after engine swap? (consists of removing battery and holding foot on the brake for half a minute)

Battery was disconnected many times but I have never known of the break pedal to reset. I will give that a shot for sure. thanks.. My buddy had mentioned he thought the computer may need some mileage put on it to reset itself, driving did not seem to help..

And to clarify it is the same engine, just new seals and timing belt..

[abscate]

A fiberscope inspection of the cylinder and valves might tell you if you have valve damage. You don't want any contact between pistons and valves, I'm guessing A valve bent and will need replacement based on that compression number

Idle it for a bit , then pull the plugs on the trouble cylinder to confirm.