M0E

Hey all,
I have an 04 3.8 V6 mustang and I'm noticing the car idles pretty steadily between 800 and 1000 RPM even after the car is warmed up to normal operating temp. It just feels odd to me because all cars I've owned idel at about 500RPM when the engine is warmed up.

Another thing I notice is that the RPM gauge jumps to about 1500 when the A/C compressor kicks in for like 1 second and come back down to about 800.

I was wondering if anyone else with the same car had the same idle rates and the same behaviour when the A/C compressor comes one.

Any help is appreciated.

Thanks

kapone86

I have this exact same problem, anyone have any info on what it could be before I start tearing it down?

Thanks.

kapone86

Yes it is supposed to kick up when the A/C is turned on for a second or two and then come back down, but the idle itself isn't supposed to be that high. I have the exact same year v6 mustang with the same issue.

08'MustangDude

There is a RELEARN idle trim process. You should do it any time you change the intake,
or tune the car. It also involves turning on the A/C in the steps, but I didn't do that, I just
let it learn the throttle trim from cold to operating temperature. Since you have an IAC,
it will still learn.

Wait till the engine is cold.
Disconnect the battery, and touch the + to the -.
Reconnect the battery and start the car, and let it idle to operating temp, about 15 minutes.
Then turn the A/C on, and wait a few minutes.
Turn the car off, and on, and the idle should stabilize right away.
Turn A/C on to test where it jumps.

If you still get the same problem, you may need a new IAC valve.