IAC and air conditioner

[k_brute]

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!

 

[Aeroman]

Check the IAC

What happens when you "pull" the plug on the IAC ? engine speed should drop & recover only when you plug the IAC back in. Do this several times, If nothing happens or the recovery is erratic, you should consider putting in another IAC. Make sure the electrical connector is clean & in good shape (no corrosion or damaged wiring).

 

[wmburns]

First read #3

http://www.stangnet.com/mustang-forums/810729-starts-but-dies-idle-help.html

Next, what is the condition of the AC charge? If the AC is short cycling due to low freon, the PCM will not have enough time to learn the correct idle trim values for AC operation. This will result in near stalling as the compressor cycles on/off.

 

[k_brute]

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.

 

[wmburns]

vacuum leak=bad running car

Today's cars will not run right when even the TINEST vacuum leak. To all of you guys out there having problems with how your car is running, let me repeat.

Today's cars will not run right when even the TINEST vacuum leak.

The PCM can not compensate for a vacuum leak.

Even something a small as the oil dip stick not fully inserted can cause issues. When inspecting for vacuum leaks, look at the condition of all hoses, seals, clamps, tubes. Clean? Tight? Are the hoses dry rotted?