1991 300SL...goes instantly to 2,000 RPM's upon cold startup then drops to normal. Starts normal the rest of the day.

This condition started a couple of years ago. I found that I could remove the air cleaner cover & spray "Air Intake System Cleaner" into the throttle body-butterfly/throttle valve area then wipe it clean to remove any carbon buildup and it would then start normally for 2-4 month & then I would have to clean it again.

Now the cleaning process no longer works.

I have now experimented (with the air cleaner cover off) by pressing on the throttle valve to make sure that it is free moving & then starting the car & it starts fine. But, the problem is still there when I start it the next day without doing this.

It would almost seem that there could be carbon build-up underneath the throttle valve in an area that I can't get to. I can barely see a moving arm done there that could also need cleaning.

Any suggestions.

Earl