idle speed surge '00 with 3.8L 100K mi.

[rhe]

I have an intermittent throttle surge when in Drive / Reverse, and I remove my foot from the brake. This may help my intent to send this car off a high cliff, but hopefully without my presence.

It will jump as if I tapped the throttle (up-down) and sometimes repeat (up-down-up-down). Engine Temperature, and air temp. don't matter, but it never happens from a stop light (how does it know??) only in parking lots. Maybe it is related to a change in gear selection; I'll have to experiment for that. I've checked the electrical connections and for dirt deposits on the IAC, throttle plate. MAF. There are no obvious signs of a vacuum leak.

By the way, the engine runs well in every other way. I recently resolved an intermittent engine miss (low RPM) that is related to Bosch platinum spark plugs. The factory trained technician is now studying a recording from my car (flight recorder), but my expectations for Ford analysis is very low. Typically they say "No codes... can't fix that..."

My brother-in-law suggested that I look at some valve on the brake assist vacuum line, but my Haynes manual doesn't expand on this.

Thank you very much for any help.

[RahX]

the brake booster, which is connected to your master cylinder, has a big vacuum line going to it. there is a plastic piece on this vacuum line that holds vacuum in the booster. start and run the van for a min or so and shut it down. unplug the hose from the booster and listen for it to suck air. if it does then dont worry about that. the 3.8s have a problem with the upper plenum o-rings leaking. MIGHT be your problem but they usually set a code. also the MAF might need to be cleaned but those usually result in a dead spot when youre on the gas but they can affect idle quality.

[rhe]

Thanks!

The O ring seals were replaced along with several other TSB upgrades under extended warranty. I'll look at that vacuum valve the way you suggested. It sounds like a cheap component, do you know if it can be replaced separate from the booster?

[rhe]

Solved !
An Idle Air Control replacement solved ths problem. The engine would throttle up momentarily when I took my foot off the brake in parking lots. The throttle surge created a danger of running into something. It would never happen on the road, such as when releasing the brake at a green light.
The the "parking lot" association was caused by steering pressure demand. The engine control sensed an increase in power demand and tried to tweak the IAC in response, but it would stick momentarily, then release with some overshoot; this caused the surge in RPM.