My 2002 E430 knocks @ idle when in gear only. My mechanic told me it was carbon buildup. He put some product in the fuel which fixed the problem temporarily, but it's back.

The knock is equal to engine speed when the car is in drive or reverse @ idle. There is no knocking with acceleration ever.

Has anyone had this prblm? Is it REALLY carbon builld-up?

I use premium only - always.

 

If it is a carbon build up I would say go and blow it out. BY this I mean do you drive it on the highway at all?

 

oh absolutely. I drive 22 miles each way every morning - all highway. I've been known to go a just a little faster than posted speeds too . . . .