On a couple of mornings now I have a weird problem when I start up the S. The RPMs shoot up to around 2500 and then drop to 2000 and starting bouncing this way. The engine feels like it's running rough and struggling.

On the mornings that it starts fine, the same thing will happen when I give it a little throttle: http://www.youtube.com/watch?v=HxwQAmMOsqI

As the engine warms up the issue starts to go away, but there's usually noticeable lag whenI hit around 2500-2800 RPM.

Ideas?

Thanks!

Edit: car is all stock

 

After some more research, stuck or dirty IAC?

 

Not sure I got anything out of that vid. Did the bouncing occur from you hitting the gas just once or was it just a constant pressure on the gas pedal?

 

Constant and steady pressure. Kept bouncing until I let off. And some mornings it will do that while idling without me touching the gas.

 

Caught it doing it at idle without me touching the gas!

Video

I'm not sure if it's coincidence, but every time it has done exactly this, the of the car was elevated on jack stands for a few hours ...

 

Stuck IAC rotary valve, guaranteed 100%.

 

Thanks!

Possibly stupid question, but: It's a 2007. I'm looking at my Helms manual and it appears there's no IAC valve on '06 and '07s?! I see the throttle body has seen some changes...

Left shows '00 to '05, right shows '06 and 07:

 

Do you have an engine management light on? I have the same issue exactly and people are suggesting it's the 02 sensor, although I have and engine management light on...

 

Nope. CEL is off. I suppose I'll stop by the dealer tomorrow and get their "2 cents"

 

Year would have helped yes, so no iac is not the problem it doesnt have one.