1992-94 Audi Problems

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.
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But if you have the V-6 engine, there is a pressure relief valve in the head that goes bad and needs to be looked at. This will cause loss of oil pressure to the lifters.
Mr. Shiftright
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- Complete tune up: spark plugs, cap, rotor and wires
- Replace valve lifter to fix the knocking engine noise
However, he does not believe that an engine oil additive would fix the valve lifter noise since the oil was changed only 800 miles ago and looks clean. The car is also driven daily to work which should free a sticky lifter. Anyway, if it helps I would like to try using an additive to save the repair cost of replacing the lifter (approx. $200 by his estimate). But I am not sure if an additive would help. Any suggestions/recommendations on additives?
You have to remember, just because a person works on one type of German car, that does not mean he knows how to work on another.
First things first, the most obvious first and then work down to the more obscure.