96 windstar 3.0 rough idle

I have a 96 windstar gl with a 3.0
It runs great except when you have the the heat or air on, it will rev up about 4 seconds. If it is on vent or floor heat it won't do this, but will on any other setting. I don't know much about vehicles but if you guy's could give me suggestions as to where to start I'll try and see what I can do myself, if I can't figure it out I know a couple of guys that might help out if I just know where to start.

THANKS!

In certain "heat" settings, the air conditioning is ON.
Even in VERY cold weather. Most cars engage the air conditioning in any setting that includes any air to the defrost. My '96 3.8L engages the air conditioning in any setting except vent (dash panel) and OFF.

Now for the 4 second rev up. Mine does the same thing. Whenever the air conditioning compressor is engaged....the engine will rev up. This is to prevent stalling, or bogging down under the load of the air conditioning. As when you have the controls set for air conditioning.....the compressor will cycle ON and OFF.....with the engine rev at each ON cycle.

Anyhow, it is NORMAL. The thing that seems different about it is.....the older air conditioning units had a sensor that prevented the compressor from engaging whenever the outside temperature was below 40 or so..... With the newer type of "non cfc" refrigerant.... They no longer do this....so you will experience the air conditioning cycling on and off....in the really cold weather.....when the last thing on your mind...is turning your air conditioning ON.

Now, if you start to see your idle not correct....as in cycling up and down....sticking...etc.... Then it could be a sign that the Idle Air Control (IAC) is starting to stick. The IAC is located next to the throttle body....on top of the intake manifold (at least on the 3.8L). The IAC controls the idle speed...like a mini throttle body. When your foot is not on the accelerator.....the IAC opens to let enough air into the engine to maintain the correct idle speed. Usually, when the air conditioning compressor is engaged....the computer calls for a slightly higher idle speed.

Thanks WISWIND for your reply. I 've had this van 2 1/2 years and just noticed it a few months ago, it probaly always did it, I just never noticed. When it revs up in gear it tries to lurch forward if you're at a stop you have to make sure you've got pressure on the brake pedal. Must be I've been using the air/heat more often than usual.

THANKS!