I have a 92 Audi 100S. Everyday when I start the car in the morning, it starts rough (as if all parts are loose - sounds more like a weak rusted old diesel engine). Then in a few seconds when the RPM settles at around 800,, it gets a bit better but the noise (similar to a knock or a sticky valve lifter) is still there. I can also hear the noise go up a bit when I push the gas pedal. So today I showed it to someone who said that it was quite common in many V-engines. He said that it is probably a sticky valve lifter that needs some cleaning. He recommended an additive that cleans the valve lifters and makes them run smoother and quieter. He also suggested using a 10W40 grade engine oil for the V6 engine. He says that heavier oil will improve lubrication and reduce engine heating, but may reduce mileage. I don't remember the name of the additive he mentioned but I can ask him again. I will list the additive here once I find out. I did not find enough information on this car in the Town Hall and so I created a separate discussion. Hoping that Audi owners will list/share their problems here. Thanks.