Idle Air Control Valve

[NPdarkside21]

I am currently having an issue with my RPMs staying high after throttle and upon startup. At startup, it hits over 2k rpm and then trickles down very slowly and sometimes the rpms stay high after accelerating and coming to a stop. I tested to see if it was a possible vacuum leak by unplugging the IACV and it drops to around 500k rpm but as soon as I plug it back in it rises. It does eventually drop to the desired 500rpm range when it is warmed up but intermittantly does not. I cannot figure it out. Throttle body is clean, new IACV, new throttle position sensor, no vacuum leaks, and it's a 1999 XLT with >1000k on this new 3.0L motor.

 

[franklin2]

You always have the old capacitor trick. The capacitors go bad and leak inside the ECM. I think someone fixed their idle problems before by replacing these. You can open the computer up and take a look.