Neither.

__________________

Gone to the dark side

- Jeff

GM has a potent cleaner that you spray or pour into the intake while the engin is running, then let sit awhile and then drive around smoking up the neighborhood. I haven't used it in years, but the part number is either gm12378552 or 1052626.

__________________
Prost!

This engine takes non resister plugs H9DCO Bosch available att the dealer or the NGK non resister plugs. other type of plugs will leave the engine with a low performance. The spark plug end connector covers do become conductive over a period causing a slight miss ,readily checked by the corona discharge ring on the plug porclean .
mak
300se

Thanks to everyone for the great recommendations. It sounds like I should put in a good top cleaner into the car and then change the oil and run it for a while to see if the intake and exhaust valve problem resolves. If not, it sounds like I need to remove the head and do a valve job.

Any recommendation on a good shop manual for this car? What is GM top end cleaner mentioned above and where can I buy it? Thanks.