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Odd Idle Issues

I was having issues with engine RPM dropping out and occasionally stalling on idle. I went through the normal procedure to set everything correctly. Cleaned the IAC. Got the car warm, idled with the IAC unplugged, set the idle RPM to 750 with the throttle stop. Shut the car off and disconnected the battery to clear the KAM. Adjusted TPS voltage to 0.94V, at least the best I could. No dead spots in the TPS, but a little finicky at the bottom of the range, could go as low as 0.8X V, but as soon as you start to move it, it goes quickly up to 1V and moves smoothly from there. IAC was resistance checked, and got 11 ohms, within spec.

After all that I started it up, and it idled lower than expected, around 1000 RPM. Where it gets really odd is after it warms up then it somehow idles even higher, at 1400 RPM. The IAC moves nice and freely, and I cleaned all the carbon out of it. I can tell it's working due to the significant drop when unplugging it, but it's almost like it's not functioning as it should. Any bench tests or other things I could check before possibly replacing it?

Seems you may have an issue with the TPS if your voltage jumps at the low end...

Remove the TPS and try some electronics cleaner like deoxit to see if you can get a smooth voltage reading at the low end of the range or replace the TPS. The IAC is most likely not causing your issue especially since you have an unusual reading from your TPS in the idle/low rpm voltage range.
1987 TC, 5sp, BoPort Stage 3 Head, 2.1 Cam
1996 Impala SS

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