'86 Country Squire idle problem at start

[patrick66]

On my '86 Country Squire, I have an idle problem when the car has first been started from cold, and the first minute or so of idle in gear. It has 76K miles.

When the car is first started, the idle goes up to what sounds like 2,000 RPM or so if the A/C is ON, and about 1,500 or so if it's off. I'll drive to the end of the driveway and open the entry gate, putting the car in Park in the process. The car will now have an idle that varies from roughly 500 RPM to about 1,500 RPM, whether or not the A/C is on, and it'll either act as if it wants to stall and die, or it will die. Restart the car, no problem. Driveability is not affected. I get direct on the main road, then the Interstate, and have no problems.

I've heard that converting the A/C on these to R134 can cause this very problem. Anyone familiar with this issue on the mid-'80s Panther cars WITH EFI? My son's '85 Grand Marquis (with the throttle-body FI) does NOT have this problem, and his car has been converted to R134, as well. His car has 39K actual miles on it.

I've also heard the IAC might be at fault. How can I determine this?
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[gadget73]

Its not related to the AC.

It sounds like a vacuum leak or a sticky idle control motor. Often, cleaning it will fix this sort of thing. Its a cheap thing to try if nothing else. If the vacuum lines are all original, change them. Leaks make the engine idle stupidly, and cause other running issues.