how do you disconnedt the air-injection pump? my 1997 e320 does the same knocking noise sometimes when the car is cold in the morning. i was starting to think it was connected more with the oil lifters. i was thinking of adding a engine cleaner product before doing the oil change, but i need your guys' advice first. is this recomendable? if so, what what be a good product, like bg or lucas? please help