High idle, big mystery

(This is copypasta from AllFordMustangs. I promise I'm not a bot, I just posted there first)

EDIT: This turned out to be the Idle Air Control Valve. I replaced it, problem solved.

I have a 95 3.8, the other day I noticed all of a sudden it was idling high. I had been going down a 35 MPH hill and I was in 3rd gear to help keep my speed down, pulsing my brakes. When I threw it in neutral and stopped at the bottom, the revs never went down. It usually idles just under 1k but now it's around 2k.

I've tried spraying CRC all over the place, but no dice hearing any revving up. I also cleaned the IAC valve, and I tried testing the IAC and its plug with a multimeter. Got 12-ish ohms on the IAC, and 12-ish volts on the plug.

I took off the air duct and looked at the throttle plate, and it does look closed to me. When I push down the gas pedal I do notice a little sort of pop, like I'm overcoming a very tiny amount of resistance to opening the throttle. I did unplug the IAC while running and nothing changes.

I really don't want to spend the money to take this to a shop, but I'm running out of ideas. Any suggestions are greatly appreciated!

Noobz347 said:

If you were a bot, your promise would be meaningless. :not: I do trust however, that a bot does not have an issue with his 3.8L 95 Mustang.

The very first thing I'm going to as is whether you pulled ECU codes.

Click to expand...

I'm going to assume those are the same codes you get from the OBD2 port with a code scanner. In that case yes I did, at one point. I went to unplug the MAF, on somebody's advice, but got the IAT by mistake, which tripped the MIL. So I pulled codes and the only code was for the IAT.

Solved it! Went ahead and replaced the IAC valve and that fixed it.