Black_06GTStang

I have a weird issue with the idle. I noticed it when the weather was getting colder and starting using the heater. With the car stopped the idle would drop to about 600 or so rpm, catch and go back up to around 800 and hold. The car wouldn't stall, just mildly annoying.
Today, I started it up and let it idle for a while. I put the heater on again, but noticed that if I had the hvac setting on anything but defrost, it idled rock solid. As soon as a defrost setting was selected, same thing, idle would drop, catch itself and idle fine and then repeat. I don't recall this happening before the supercharger and subsequent tune. Could it be a tune issue?
Any other ideas? Thanks in advance.

302svt

That is the A/C kicking in. It is set to come on in defrost mode so it will run some in the winter, you should see your A/C light come on when you go to defrost.

Black_06GTStang

Thanks 302. I think that's exactly what's happening. The a/c compressor is kicking in. From what i've been told it is putting an excessive load on the engine. I have a local club member looking into a Ford reflash to perhaps fix it. thanks for the feedback!

exx1976

Hrmm. Good to know. I don't make a habit of driving my car in cold weather (snows a lot here). However, I have had cause recently to take it out a few times to take it to various shops to have work done on it, and I have noticed this issue. I, also, didn't notice it before the supercharger install. But, I also didn't drive my car in the winter at ALL prior to getting the supercharger (doing lots of work to it for an upcoming indoor show)..

VerginaStang

This happens to me also- I figured it happened to everyone bc everything works correctly- defroster still defrosts lol. It does make that pssst sound every so often though.

07vtgt

The AC comes on during defrost to help remove some of the moisture from the air which is on the window causing the fog. completely normal

Black_06GTStang

I completely agree that it's normal for the ac to come on during defrost, but what i'm not sure is normal is that the rpms drop by about 200 when it does kick in. Feels like the car will almost stall, then catches itself.
If I can get any further info, I'll post back.