High Idle Saga Continues...

[rycodge]

I think all signs are beginning to point back to a faulty IAC valve. Here's why:

1) Everything appears to be functioning normally except the IAC valve (evident when it's disconnected - engine idles great)
2) I cleaned my original IAC valve with no luck
3) I replaced my original IAC valve with a part from Autozone
4) I suspected my replacement from autozone was defective so I replaced my replacement IAC valve.
5) I've performed the idle relearn procedure a dozen times.

I'm about to break down and order a motorcraft IAC valve... They have them on amazon for a good price. Is there anything else that you guys think it might be? I've 99% ruled out a vacuum leak. The car runs great besides the high idle problem.

[FocusGhia]

Check to make sure pipes from charcoal/purge cannister (usually on bulkhead) are not broken or split.

[whynotthinkwhynot]

Why not see what price our vendor Village Ford can give you? Support those who support the site! I'm not asking you to spend more money, just see what their price is. It should be lower, but IDK what you found it for on Amazon.

[rycodge]

Mystery saga continues with a major update!

So this car had a previous front end collision and some repair work was done to the wiring harness that runs through the front part of the frame. My right hi beam light wasn't working and traced the issue to the wiring harness. The incompetent idiots that "professionally repaired" the car swapped the green-orange hi beam power lead with the green-orange lead that goes to the AC pressure switch!! It looks like the pressure switch wiring was also severed and rewired together. My hi beams work as expected now...

Here's the kicker. I'm wondering if my AC pressure switch / wiring cluster is telling my ECU to crank up the idle even when my AC is "off". I am under the impression that my idle control valve is working just fine, it's just being told to raise the idle when it shouldn't. Hence, when it's unplugged the car runs and idles normally.

Am I correct that the power steering switch and one or both of the AC switches can make the ECU crank up the idle? Can I bypass the switches and hotwire the car quickly to make it think the AC is truly off (It's winter in oregon, no need for AC!).

Also, if anyone has a detailed wiring diagram of the AC pressure switch / wiring that would help a ton! The haynes diagram is a bit lacking in this area.

[whynotthinkwhynot]

I don't have detailed wiring, but typically you just put the same colored wires together, and life is good. You can also continuity test wiring to be sure you're dealing with the same wire on both ends.

Yes, power back-fed through the AC circuit would boost idle.

[rycodge]

I've solved half of my problem. It turns out that the power steering pressure switch pigtail was simply not hooked up to the wiring harness (it's wires were just stuffed into the plastic wiring sheathing, not soldered to the correct wiring).

Here's the thing though - My idle is still relatively high. Fully warmed up the car will idle around 1400-1500 rpm while driving down the road with the clutch depressed. This is much better than 2200 rpm which the car was experiencing before. The PS pressure switch is indeed working, but it gives a "mega boost" up to like 2100 when turning.

I'm almost positive the ECU thinks the A/C compressor is engaged and raising the idle. Problem is the car (and wiring harness) was damaged previously and I'm missing the pigtail for the A/C compressor. I've tried removing the A/C fuse and relay, but that has not helped at all.

Here's my question - Which wiring harness does the A/C compressor plug come off of? I've noticed there is a spare clipped wire in the harness with the O2 sensors and the power steering pump switch. I do not have spare wiring in the "main" harness that contains the headlights, turn signals, etc.

[emsvitil]

The ECU may be keeping the IAC valve open if you're moving for smog purposes, thus the high idle with the clutch in......

[rycodge]

The ECU may be keeping the IAC valve open if you're moving for smog purposes

No offense, but I would like a bit more of a concrete answer on this one

I could see idling at 1000 or so, but whether the clutch is in or out (neutral) the car idles at around 1500 rpm until you come to a complete stop. This morning in the cold when I started it up, the car jumped up to 3000! Seems way high even for a cold start.

Would a scan tool be able to check if the ECU thinks the A/C circuit is on when it is in fact off?