Not sure how you've diagnosed that the IAC seemed to be in functioning order, however, a good test is: Use a little bit of throttle opening to help the engine idle. If this helps it run where it otherwise wouldn't then likely you have taken over IAC'* responsibilities where it has failed.

X2 ^ Even tho I keep my bay clean & lightly wash occasionally, I am very careful about covering up connectors and Alternator etc before hand.

Yah. Just put in the new ECM and, although it fired up quicker, it'* still idling rough and racing the RPM once it warms up...

Drove it to the parts house and back to order the IAC valve. New ECM didnt do anything. Guess I'll report back tomorrow evening after installing the IAC.

Im sorry to hear that. But racing RPMs? I had that issue, too. It was solved by my ICM and IAC. key word on the and. also, check vac leaks, i had a hose down by the trans and the little black distribution block on the intake causing pretty bad vac leak. also the PCV grommet, I had that unseat and that caused a vac leak. the tube going to it prob can rot too.its really freaking dumb on these era cars. i can try to find the dorman pn for pcv... but its been a while. and it was a BITCH to replace

It wouldnt affect the racing RPM, but your thermostat is too cold. esp with winter coming. you need a 192 or 195 iirc from memory. That would just be long term fuel and condensation and mpg but anyway.
Have you checked your throttle body gasket and had it off at all lately?

and your TPS, the codes are saying its getting 5v then 0 volts or somewhere close without any articulation of the throttle. The sensor sounds bad. it uses TPS for fueling and transmission shifts, or maybe just fueling(1989 i dont think had electronic controls on trans)
34 is the same as 44 which if your throttle position sensor is causing your car to overfuel, under fuel(with open throttle plate, might try to open IAC while throttle is open, causing lean) , advance or retard your spark, etc. it cant accurately control combustion. But on 1989, you got one o2. disconnect it. i drove the car first 6 months owning it and never could tell it needed an O2 sensor. it ran barely different. better MPG for sure but the corrections back in the day were less noticeable. This will simplify your diagnostics. if you notice an improvement or you solve the issue unplugged, and it comes back plugged, you can figure that as a bad part. i would try without it for sure. and did you check engine grounds and the connector for corrosion?

also, is your throttle linkage free and not binding? is tb clean? plates could be sticking open. Has anyone touched the stop screw on the tb? It is not to be adjusted.

What is the story on the battery on this car? Is it a new unit since the car is being brought back on the road after such a long time?

As also mentioned, I would be looking for a vacuum leak, and given it'* starting to smoke blue, it'* possible it could be starting to burn oil. I would be focusing on the PCV area. If the Transmission Shift modulator is leaking however, that can also cause a vacuum leak, and the car could ingest transmission oil.

It also may be good to review all of your primary power sources and grounds to make sure there isn't corrosion and that connections are good. Power issues can cause gremlins that will make you chase your tail like crazy.

Yeah I still have the OEM 195⁰ thermostat. That was a temp solution while it was running poorly at full temp for a while.

and your TPS, the codes are saying its getting 5v then 0 volts or somewhere close without any articulation of the throttle. [/QUOTE]
Ive tested the sensor and it reads .42v closed and 4.6v wide open with a smooth transition up and down.

No change to how it runs plugged and unplugged.

Grounds seem like their ok. Pulled the two on the back, cleaned and reattached. No change.

TB has been cleaned. If you're talking about the idle screw, unfortunately when I got the car the nut that backs up against it to keep it from moving was gone. Replaced with another nut and it hasn't been moved since.

New battery. Strong voltage. All cells good.

New PCV grommet and accompanying vacuum lines.

Yeah I think this is my next logical step if the new IAC valve doesnt fix anything. One by one trace every connector from sensor back to the ICM to check for possible broken wires.

Ive tested the sensor and it reads .42v closed and 4.6v wide open with a smooth transition up and down.



No change to how it runs plugged and unplugged.

Grounds seem like their ok. Pulled the two on the back, cleaned and reattached. No change.



TB has been cleaned. If you're talking about the idle screw, unfortunately when I got the car the nut that backs up against it to keep it from moving was gone. Replaced with another nut and it hasn't been moved since.



New battery. Strong voltage. All cells good.



New PCV grommet and accompanying vacuum lines.



Yeah I think this is my next logical step if the new IAC valve doesnt fix anything. One by one trace every connector from sensor back to the ICM to check for possible broken wires.[/QUOTE]
new plan: check out your TB. If your screw was missing... how much you wanna bet someone was playing with it and didnt put it back together right or wore the shaft down and now it cant meter air. i would look at an identical junkyard car if you can. i wish i pulled the TB on my cousins 88 lesabre when i had the chance, i would give it to you. i can show you pics of mine???? show me your engine bay?

Did you specifically get the ground under the ICM? can you give us pics of each quadrant of engine and the big important things like your pcv valve, sensors, firewall relays, battery connection, vac lines, tb, grounds, etc. egr valve