High idle/revving problem - doesn't seem to be the IAC

Ok, this is wierd. Searching has simply prescribed replacing the IAC, but that's not working.

Problem started as a high idle around 1000 rpm, put it in drive and it'd drop a bit, but still high. Parked it overnight and went to drive to work yesterday and it started up, went to the 1000 rpms as before, but when I put gas to it to drive forward it shot to 2000 rpms and stayed. I could give the pedal a push, revv it up and it'd come back down to 1000 rpms, but after a couple of seconds the IAC would buzz and bump the rpm back up to 2000.

Every other time since the problem started, it will not fire up without depressing the gas pedal. Sometimes it fires right up. It does this inconsistantly, but does it just the same.

Where does the IAC get it's signal source? I've replaced the entire throttle body with another that was off an engine that ran fine - it still does the same thing. I've replaced that second IAC with a 3rd and it still does it. Granted all the IAC's have been used, but seems a whole lot unlikely that I have 3 bad ones. I replaced the TPS a month ago.

Help!

Thanks in advance! :thumbup:

Have you checked / cleaned all your grounds? Checked for vacuum leaks?

LOL - disregard. Fawkin' thing was messing with me.

Up to this point, it hadn't set an engine code which I thought really odd.

I go out there after posting this and fire it up, does everything it had been doing before and ........... finally sets a code. P0121. TPS!

I just replaced that damn TPS (granted, with a used one) last month! But the symptoms this time were totally different than when the first one went out.

Another used TPS in it - runs fine now.........(fingers crossed).