I had this done on my car when I moved to Ontario because the car wouldn't pass the hydrocarbon test that is part of the emissions certification. They did the Motorvac and then told me to drive the car really hard for a few days to burn off the residual chemicals and loosened up crud. I did and the car passed - by one point. A pass is a pass I guess, but I still have a rough idle I can't get rid off. If anything it seems to be worse after the Motorvac. My new Mechanic said it was probably a clogged injector or something and suggested I try one of those fuel treatments. I used Castrol Syntec exactly as directed with no results to my rough idle. I do know that Motorvac must clean yuour engine quite well becuase after they did it on my car and I drove it hard for a few days I changed the oil and man was it dirty (only two months old). I couldn't believe it. I suggest if you get a motor vac done to change your oil shortly after

__________________
Jason Priest
1999 E430
1995 E420 - retired
1986 420SEL - retired