2002 Taurus high idle

I have viewed many of the posts about P1506 and high idle but still have not found the cause. It started after I replaced plugs/wires. Since TB was off I looked for carbon and smooth operation, looked good, plate seats good. I noticed some vac leaks at hoses during tune up so I put clamps on them, hesitation at acceleration went away but the high idle started. I replaced the IAC, cleared code P1506 with code reader and disconnected the battery for a few minutes. No joy. Engine hangs at 1300 rpm after I let off pedal for about 6 seconds then drops to 1200 for a few seconds then stays at 1000. Needless to say this can get hairy in traffic. I removed the intake plenum, cleaned the gaskets, the big EGR port (and the tube), checked hard plastic lines for vac leaks, rubber hoses for leaks/cracks, reinstalled everything, still idles high. Am wondering if I buggered up the wiring to the IAC. Not sure what is supposed to happen when you disconnect the IAC when idling, change or no change in idle? I get no change in idle. When AC is switched on, an minor decrease initially (a second) then bumps back up. Engine idles smooth, runs smooth, just idles high. Pretty much at a loss here. Any thoughts/suggestions are greatly appreciated. Thanks--OOOPs! sorry wrong forum, been hunting thru all of them tonite

Per the factory service manual, Diagnostic Trouble Code (DTC) P1506 indicates Self-Test has detected an IAC overspeed error.

Possible causes:

-- IAC circuit short to GND.

-- IAC valve assembly stuck open.

-- Vacuum leak.

-- Damaged IAC valve assembly.

-- Damaged throttle body.

-- Damaged PCM.

With the IAC disconnected I would expect the car to want to stall. If it continues to idle high, I'd continue searching for vacuum leaks or something preventing the throttle plate from closing completely. Since you had the throttle body off, are you sure you got the throttle linkage connected correctly? I know you say the plate seats well, but is is pretty much completely closed or can you see a gap between it and the wall of the throttle body?

-Rod

Thanks Rod, I'll keep looking.

Just a follow-up...It was a vac leak at the PCV valve. Original valve with 160k+ must not have liked being disturbed during tune up. Thanks for info Rod.

Good find. Thank you for the follow up post!

-Rod