I think I've seen stuff they actually sell that you put in before a smog check, and they advertise it as such.

Not sure..

I would use a good fuel cleaner, change plugs, maybe air filter, and go again....

Alon

__________________
'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon