Hi guys,

I have a 2004 Volvo S40 with around 150,000 miles.

About every 20th start, the car immediately stalls if I don't feed it gas and keep my foot on the accelerator.

Remove foot, immediate stall.

I have found through trial and error that if I rev the car incredibly high, just up to the red line, I will hear/feel a clunk, and then the car will idle successfully.

No check engine lights etc. My mechanic cleaned the throttle assembly as he said it sometimes can keeps an air intake valve open, and the thunk could be that valve closing.

Any other thoughts on what to do to resolve this?

 

Have you checked the PCV valve? If not, check it and make sure that it is not clogged and vacuum is not leaked.