talon39 said:
. . . The engine runs strong while driving but idles a bit rough. Especially in drive with the air on. It sometimes stalls out when I am slowing down for a traffic light, not very often though. The idle seems a bit low as well, in drive it can be as low as 300-400rpms. However after driving for 40min. in stop and go traffic, then stopping and putting it in park, the RPMs sometimes go up to 2000 and stay there. Which seems way to high. Very strange. . . .
I didn't see (could'a missed it though, it's early) that anyone had suggested inspecting your TPS settings -- While the IAC is the control mechanism for idle, the ECU looks at the TPS's output to determine that you actually wanna idle... That data, coupled with an "in gear" signal from the NSS causes the RenixII ECU to try to drive the IAC.
To me, IMHO, your symptoms describe a TPS that isn't happy, that, coupled with the fact that they often fail as a result of washing underhood (exterior throttle body cleaning with solvents on a warm motor, being a most rapid cause of death), which you mention, but not it its timing relationship to your symptom.
The TPS on an Automatic of your vintage has qty=2 connectors a flat on (with all of the contacts in line) and a square one (contaces form a square). The flat one is what your ECU uses for "throttle position" including your desire to "idle", while the square one is used by your TCU (Tranny Control Unit) to determine data needed for shifting - - The service manuals (and, to an extent, threads here) describe how to set the TPS, so I won't go into it, BUT I highly recommend examining the output characteristics of the ECU's portion of the TPS (the procedure for setting the Auto Tranny TPS involves only the tranny connector, so errors in the ECU"s portion of the sensor often go undiagnosed!).
Quick look at what you should see:
* leave the connector connected (remember we're talking about the ECU's flat 3-pin connector here)
* backprobe the connector without disconnecting it (did I reitterate?)
---- with the key in "run", best if the engine isn't running, and the throttle plate closed, you should see
-
pin A - 5vdc - you can measure to any ground, though the connector's ground is on pin B
-
pin B - Ground - measure it anyway - it has been known to go bad - you can splice another ground in if you'd like)
-
pin C - something less than 0.9Vdc - The ECU will look at values at and below about 0.9Vdc as a "no throttle" signal and try to control the idle as above... Don't leave this pin yet watch the voltage output as you slowly open the throttle (see, I told you "best if the engine isn't running") you should see the output voltage slowly
and smoothly increase from where you start to something much closer to 5Vdc (usually you'll get to the 4.7voltt area - that's fine)
-- If you don't see the output moving smoothly over the entire range, chage the TPS. If the output is at a volt or higher (using the pin B as ground) then set your TPS's TCU connector's output values as describe in the FSM (or many posts here) and re-verify the ECU's connector's output values... If it's still over a volt with the throttle plates closed - then the TPS should still be replaced.
Just thought I'd toss that in since nobody'd posted about the TPS possibility