My newly purchased car is a 1995 Audi 90 Quattro Sport with a 5 speed. The car runs great normally, has a few problems with such things as RF motor mount and the A/C system, which I'm working on. I am having a problem under acceleration that has led me to notice some other problems. Under heavy acceleration around 4000 RPM the engine will seem to hit a flat spot. The car won't accelerate, the revs will remain the same, and my foot is still on the accelerator. This led me to check out the engine some more, and I am now hearing an RPM dependent clicking, although I can't tell where it is coming from. I'm thinking valves probably. Also, during the checking of the engine, I noticed that from idle, if I hit the throttle a decent amount, the engine will make a very deep throaty sound, and some smoke will come from the tailpipes. I don't know if this is just how the engine works, if it runs rich at low RPM in order to give acceleration. There is also a whine that is RPM dependent, and I would describe it as air escaping from somewhere, but it could be anything I suppose. There is also a smell coming from the engine compartment, it gets stronger under acceleration, and is somewhat sweet smelling, but it isn't antifreeze. Any help would be greatly appreciated, thanks!!