IAC and air conditioner

Hi guys,

First time posting in the forum, but a long time reader!

My mustang has been having idle issues for awhile now (dropping to around 500 and revving back up to 800 or so when coming to a stop). I replaced the air filter about two months ago and this seemed to solve the issue with engine bogs. I reset the PCM at the same time by leaving the battery unplugged for a half hour to re-set the idle speed.

Since its gotten hot lately, I tried to run the A/C a few days back and the car almost stalled out when coming to a stop (dropped to around 400 rpms) but gave it gas to save it. It idles normally without the A/C on. This only happens when the compressor is engaged on the A/C. The A/C is ice cold when it is on and the car runs fine otherwise.

I'm thinking of replacing the IAC since it has already been replaced once on this car at around 25,000 miles or so. From my reading it seems there is at least one solenoid connected to the IAC that directly relates to the A/C (fast idle control device). Are these solenoids separate parts or integrated with the IAC unit? Do mustangs even have a FICD?

Any advice is appreciated before I go spending my life away replacing parts!

A/C charge was checked yesterday and it was at normal levels.

I actually went to the dealership (argh) yesterday to drop off my spoiler for repainting and had them take a look at some things I thought were unrelated. I had them replace a vacuum hose that was looking a little ragged. The car in general seems to drive better after this. Not only that, but it also seems to deal better with the A/C being on. No more RPM drops at idle. Maybe the PCM just had to learn or couldn't compensate for the vacuum leak?

The A/C still drags on the engine when it comes on, but its always done that unfortunately. Must be a design flaw for the car in general.