Seafoam

There is a product called SEAFOAM that works great as a fuel system cleaner as well as a top engine cleaner. I don't sell it up you can get it at many auto parts stores. You find a vaccum port( power brake booster hose works great) and slowly pour 8 oz into the hose with the motor running. Shut the motor off for a few hours then take it for a long drive. It will smoke like hell for the 1st few miles as it burns off the crud in the intake system. Smoothed out the idle in my wifes Sil very much. Runs smooth. About $5 a can.

I've used this product before...I beleive in the crankcase oil...to "temporarily" quiet down a noisy engine prior to sale. As recommended by an auto parts guy