Just wanted to follow up.

I had a high/hunting and rough idle issue after the following:

ignition: cap, rotor, module, pickup, wires, plugs
fuel: new injectors, fuel pressure check, fuel filter, gas tank purge system check
vacuum: 18 inches, no leaks found, EGR closed, PCV system working
sensors/ecu:new IAC, re-manufactured Cardone ECM (came on car from previous owner), all sensors changed except TPS (no error codes)

I was going a little nuts and I had already spent considerable time, effort, and money so I decided to buy a used but known working ECM and a new TPS.

This solved my idle issue. The car drives great. Here's a few notes:

1. There were no error codes
2. I first changed the ECM. I immediately noted the idle issue seemed to better but not solved. It still hunted high and would not settle down sometimes.
3. I then changed the TPS but did not adjust it. I took it for a spin and the car ran horribly. I hooked up an analyzer and the TPS voltage was only 0.24V , but still no error codes. I adjusted the sensor to 0.54 V, reset the the IAC, then the ECM and started it up. The ECM was in learn mode for a while then settled down. The car ran great but still had a slight problem with the idle hunting high.
4. I had messed with the idle set screw previously and backed it off too far. What this did was put the close position on the butterflies and made the off-throttle position unstable. Sometimes the TPS read 0.54 volts but other times 0.72V. After "flicking" the throttle arm a few times, the TPS voltage would go down to 0.54V. So I brought the set screw back up to keep the butterflies near fully closed but not completely. This made their closed position consistent without allowing too much air around them so that the IAC could work within its range. I then re-adjusted the TPS to 0.54V at this new proper throttle closed position on the set screw. This was a key part of the consistent idle. The closed throttle position must sit clearly on the set screw and NOT on the butterflies. This means backing the set screw way off so that it is clear of the throttle arm. Making sure the throttle is pressed hard closed. Then bringing the set screw up until it touches the throttle arm and then maybe one or two more turns. If you go too far, too much air will come around the butterflies in the closed position and thus the IAC may hit its fully closed position and idle will still be too high. If you can visualize it, its pretty simple and will help you get everything set correctly.

Thanks for all the help from this board!

 

Tootie, gotta ask. Did you try following the IAC/TPS Set procedure?
When you do one, you need to do the other. I'm sure you got it close, but just wondering.
https://www.thirdgen.org/newdesign/tech/tpimod2.shtml

 

Thanks. Sort of.

I did turn on the ignition and then unplug the IAC but I did not use the jumper. I was advised, perhaps incorrectly, that the ECM automatically moves the IAC before startup into a specific position.

And I adjusted the TPS with the engine off, ignition on and then again with it idling. I did not check it for full throttle 4.0V

I'll check for the 4.0V but I am a little wary of "touching" the setup again for a while. The IAC steps counts are right in the middle of the range at idle.

 

I don't blame ya. Let sleeping dogs lie!

 

So true.