My 1994 530i has a rough idle. It slightly rocks the car at idle and gets worse when the a/c compressor comes on. I have been to 530i.org and understand what my problem may be. Is there anyway to know what type engine is in the car - I am not the first owner. BMW says they do not have a national data base and there is no way to tell whether the engine has been swithched out? Any suggestions for identifying M60 vs M62? Ideas about other potential causes besides leakdown (maybe I'm in denial), will the problem get worse if unaddressed (I'm now using Amoco Ultimate gas), will it get worse in colder weather, ideas to reduce roughness??? Ideas for less expensive repair than block replacement?