Help! Can't figure out high idle.
 

I bought a 96 Park Avenue base for my son to drive when he turns 16 in a few months. 150000 miles, clean car, pretty much everything works except the fuel door popper.

It needed upper and lower intake gaskets and valve cover gaskets, really hard to start when cold and would randomly idle at 1500 to 2000 rpm.

I started it up after I replaced all the gaskets and still have the high idle. I replaced the IAC motor. I tried to test the plug for TPS but the only thing I know for sure is it's got the 5v reference signal, I can't tell if the ground is good and I can't test the voltage as the throttle is moved because I don't have any pins to back probe with. I have a cheap Bluetooth scanner/code reader and I might be able to test the TPS with that. I cleaned the MAF while I had the throttle body off, which I also cleaned up. I also repaired a vacuum leak while I was putting the top of the motor back together. No other vacuum leaks that I can find.
https://cimg3.ibsrv.net/gimg/www.gmf...f7fc33db2e.jpg
https://cimg4.ibsrv.net/gimg/www.gmf...4333c9ad07.jpg


No leaks from the valve covers or plenum, she just won't idle right. It won't take much for this car to be good to go if I can get the idle fixed. Thanks for reading all this! Any ideas?

Explain.

By randomly, I meant while driving. No throttle input, just high idle while in gear. I could pull over, shut the car off, restart and it would be fine for a while. After all the intake/valve cover gaskets, plugs wires etc. it's idling high all the time.

For how long after start?

I let it run for maybe 20 minutes. I was also circulating plain water in the coolant system to flush it out. I started it up several times throughout the rest of the day. It was the same each time.

https://cimg3.ibsrv.net/gimg/www.gmf...30582f1af2.jpg
Throttle position not touching pedal

https://cimg3.ibsrv.net/gimg/www.gmf...f1035a677d.jpg
Steady push of throttle to wot, disregard that 1st blip.

What about vacuum level at idle?

So it idles fine sometimes and not others? It's important so we don't waste time. If it idles right at all then we can eliminate certain things like a vacuum leak.

I am searching for a vacuum leak but haven't been able to find one. I'm not sure what the level is because I don't have a gauge.