Surging Idle, Erratic idle

  • 1997 FORD PROBE
  • 155,000 MILES

I have a ford probe 1997 4Cyl 2.0L with approximately 155000 Miles on it.
After an engine rebuilt (replaced Main rod bearings, cyl honing, pistons & rings, Oil pump, water pump, timing belt kit, seals, filters.)
I do remember that I have also cleaned the throttle body using engine degreaser (i think this was my fault) after reassembly when started the engine it revs too high about 4KRPM for about 7 seconds than RPM drops to 2K and starts surging between 2000 and 2500 RPM as the engine is getting warm the RMP decreases but the surging still with the difference of 500 RPM. When the engine is fully warmed up (15 minutes) it keeps surging at 1000 - 1500 RPM.

i have:

Cleaned the IAC
Cleaned the Throttle body
Checked and flushed the Cooling system
Checked for vacuum leaks starting from the mating surface between the IM and Head to any small hose.
I'm pretty sure that the hoses are on the right place and tight as I have labeled every one upon disassembly.

Also, when I disconnect harness attached to the IAC the engine stalls, but when I open the air bypass screw too far it keeps idling just ok (with IAC harness disconnected) once I re-attach the harness it's back to the 1000-1500 RPM surging.

What could be the reason! Is there any cure for this particular issue?
Thank you.

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Thursday, May 17th, 2012 AT 8:01 AM

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Thursday, May 17th, 2012 AT 8:47 AM

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