engineidles poorly, but only when car is moving

[Rickey_Bobby]

yup, just like the title. 99gt will idle fine parked, but when u push in the clutch to stop at a light it will stay at 1,200rpm for half a sec, then drop to like 200rpm, jump way up, hesitate, then drop back down. Once I stop, It idles fine.
It just started this lately and I havnt changed anything on the car.

Is this just bad juju?
And how can I make it stop?

 

[Jsun3701]

Sounds like a Vaccum leak!!!!!!

 

[Rickey_Bobby]

Then how would foward motion affect the idle? if it was a leak then shouldn't it do the same if i revved the motor while parked?

 

[blacksheep-1]

It's not your imagination, it's fords computer strategy that causes it. Whenever the car is moving enough to be sensed, the idle will go up a couple of hundred rpm's, really..no BS.
Try this go put the clutch in with it running and have someone push the car, I bet the idle picks up.
A good tuner can dial this out but you may want to leave it in, I know it's annoying.

 

[Rickey_Bobby]

I wouldn't mind it going up, as long as the SOHC didn't freek out about running so fast (joke) and shoot right back to a more comfortable RPM zone of 200 rpm.
And the car has a Diablo chip that was custom burnt at a dyno shop for the S/C and I have been driving on this tune for 10 months and this problem just came up.