2002 530i runs rough in humid weather
My wife drives it and assured me she has not run through big puddles. This only happens if it is raining so it's only very high humidity that causes it. It runs very rough and spews white smoke. If you try to drive it, assuming it continues to run, it has no power. My mechanic, who specializes in German cars and has always done a great job with the car, thinks it may be caused by a blown head gasket resulting from one time when the car overheated (not severely) after the plastic radiator tank cracked. He thinks it may be only 'moderately blown' but has not done a compression test. Yes, there is a little bit of coolant loss and a bit of brown goo on the dipstick that resembles an oil-and-water mixture. Whether he's right or not, I don't see how that could be affecting only high-humidity driving. The car starts and runs great the rest of the time. No missing at all and plenty of power.