'05 Mustang Idle Surge



Ok folks…

I’m a pretty good Googler and yet I still haven’t been able to find but one or two places where my problem is described as happening to someone else, let alone any suggestions to resolving it.

The car:

2005 Mustang V6 4.0 Deluxe

The problem (short):

Idle surging

The problem (long):

On a cold start, cold morning, I expect some idle surging. With a fully warmed engine and after cruising at 70 on the freeway for 20 minutes… not so much. There seems to be some correlation between being in gear and clutch in. So if I exit the freeway and am clutch-in on the offramp, I will frequently see surging up to 3000RPM! However, once the vehicle comes to a halt, it idles back down to 750RPM. Even “tapping” the gas and revving in neutral up to 4k to “clear” it will not have the desired result.

Any thoughts or further questions I can answer or things to try to further clarify the issue?



do you ever see the idle surge when stopped? Only when coasting? Could be clutch be not totally disengaging?


No, no surge when stopped. I’m nearly certain that it isn’t clutch-related because the surge doesn’t seem to bear any relation to wheel speed. It’s not like it’s gearing down as I coast (clutch-in) to a stop, more like it just didn’t idle down when I engaged the clutch, then it zoomed upward as if I was pressing the gas pedal…