Pesky High Idle preventing 300,000 mile mark

Hello all, On my 92 Grand Caravan 3.3 I have a high idle problem that consistently trips the Code 25 (IAC circuitry). Idle at startup is around 1500 RPM's and moves steadily higher(1850+) as engine warms.
Here is what I have checked and replaced. Idle Air Control Motor Cleaned throttle body and plate and replaced gasket. Swapped out Engine Control Module(ECM) from another Caravan(exact match). No known vacuum leaks or other gasket leaks No other codes found The code 25 immediately sets itself even after I disconnect the battery for an extended period. I even disconnected the ECM and reconnected. It will show the code before I ever start the vehicle again. It sets itself when key is in on position and checks signal voltage. I am suspecting wiring. Resistance tests appear normal. I would like to get this car past 300,000 (only 57 miles to go). It starts great and ran very well before this high idle issue. For those who know a ton more than me: What would be your next steps if you were in my shoes? Thanks
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The most likely culprite here is the EGR valve staying open during idle which it should not do under any circumstances. Disconnect the vacume hose from the EGR and start the engine. using a small hammer lightly tap on the EGR valve if it is stuck it will most likely loosen itself ck to see that you do not have vacume at the EGR hose at this time as well. If the idle does not come down use a small mirror and flashlight to verify that the diaphram on the EGR is in the down position (away from the vacume port) if it is then the EGR is closed.
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ck the IAC harness connections at both ends and ck the IAC wires for continuity while pulling on the wire harness..
There may be carbon build up in the idle channel in the throttle body as well generally these vehicles start burning oil at the 100k mark and this always fouls op the works.
jdybber wrote:

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In article

Sorry, a stuck open EGR valve doesn't cause a high idle, in fact the symptom would be the exact opposite.

He's already done this and found an intermittent connection.

And the symptoms of this (again) would be -low- idle not high idle.
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