I, in past was chasing very high idle 2500 , replaced tps, egr solenoid and others and finally got it to a comfortable 1200 rpm, cold start at 1800 and then comes down to 1200 after complete warmed up. today it went to 800 or lower and died. restarts fine, but if i dont hold gas pedal it will die ??? thinking IAC ?? any other ideaas?? thanks for any help

IAC would be my first guess. If you had a disconnected battery you need to drive to over 35mph to get it recalibrated.

i did have battery out for an hour, thanks
UPDATE now wont fire, turns over like no spark. coil ? i noticed alot of corrosion when popped cap in distributor. icm looks original,

[This message has been edited by traceymac (edited 06-28-2023).]

When you crank the engine, does the tach move at all? If it doesn't, that indicates a problem... but not necessarily a dead or dying ICM.

quote Originally posted by traceymac: i noticed alot of corrosion when popped cap in distributor. icm looks original,

Corrosion inside the distributor is normal. However, where you don't want any corrosion is in any of the electrical connections. This includes the two connectors on the outside of the distributor, and the connector for the pick up coil inside the distributor. Take the connections apart, remove any visible corrosion down to bare metal, apply dielectric grease, and reassemble.

Sometimes a short develops in the 4" harness between the ignition coil and distributor. Check for continuity of the wires. Also, the two screws (or one of them) is the ground for the ICM. Loosen and re-tighten the screws to create a clean ground.

There's a way to check the pick-up coil (and it's simple), but off the top of my head I don't recall what it is.

If worse comes to worse, the ICM will need to be replaced. I'd advise replacing the pick-up coil at the same time, as it's cheap insurance. Make sure to apply proper heat sink thermal compound to the underside of the new (or re-installed old) ICM.

thank you, good info that i will do !

Testing Pickup Coil in GM Manual
Remove the pickup coil leads from the ICM
Using a Ohm meter:
*Check one lead for the coil to the distributor (ground) - must be 'open' or infinite.
*Connect both coil leads and should read one steady value between 500-1500 ohms. Flex the leads to see if intermittent.

Adding to the above, you can use starting fluid to see if the problem is fuel or spark.

When you turn the key on, you should hear the fuel pump run for 2 seconds. If you don't the fuel pump relay is probably bad.

If that passes,
bump the starter quickly - not long enough to start the car or build any oil pressure. You should hear the fuel pump start to run again for a couple seconds.
The ECM activates the fuel pump relay when it sees pulses from the distributor. Those pulses are picked up by the cleverly named pickup coil and amplified by the ICM, which sends the signal down the wire to the ECM. So if the fuel pump doesn't react when you bump the key, either the pickup coil is bad, the ICM is bad, wiring is bad, ECM is bad (rare), or as above, the fuel pump relay is bad.
If this passes, it's still possible for parts to be flaky/intermittent or failing when hot, etc.
If you can then also try the resistance measurements that Vintage-Nut posted.

Without a working fuel pump relay the ECM can't control the fuel pump. There is a backup circuit that powers the fuel pump whenever there is oil pressure, but this is only a backup, it's not supposed to be the primary way of powering the pump.
Some cars have a bad fuel pump relay that goes unnoticed because the car is still driveable using the backup circuit. Then when the oil pressure sensor gets flaky, that's when the car starts acting up.

As Patrick mentioned, the tach should move when cranking the engine.