1999 BMW 3 series - strange noise after cold start/idle problems

I have a 1999 BMW 3 series, 112K, 5 speed, immaculate condition, only full synthetic oil used. After a cold start - even today at 55 degrees - I get a strange noise from the engine compartment which gets louder according to RPMs. The BMW dealer replaced the oil separator for the motor ventilator and some of the respective hoses and valves associated with it. They also checked the oil pressure when the motor was hot and cold and advised it’s fine; however, the noise is still there. (A different BMW dealer service advisor said, just after hearing it, it was an oil pump issue.)

On an unrelated note, when the motor is warm and I’m in stop and go traffic, the idle speed will sometimes go up and down (500 RPM - 900 RPM), and when it reaches 500 or so RPM, it dies. The car always starts back-up right away. Spark plugs are new and I used OEM BMW spark plugs. My thoughts are the idle air control valve.

Otherwise, the car is great; yesterday I took it on a 250 mile RT highway trip without any problems.

Any help would be appreciated. Thanks!

Why wouldn’t the dealer check that condition as rpm and oil pressure are related?

I’m not sure, Binkman. They did look for any saved codes, and there were not any. The occasional idle issue I can live with. However, the noise at the cold start is puzzling. The oil light always goes out right away, and like I said, only full synthetic oil. Do you or anyone else have any more ideas? Thanks!

You might be on the right track yourself. I just don’t like the idea of a fluctuating idle and that oil pressure issue. I have read the light is normal. Coming on and going out means oil pressure is okay. Idiot light

Idle speed.

Oil and noise… I don’t know if they are related. The old fashioned way is get a stethoscope and trace down the location of that noise even held away you could find the pitch… Watch the fan and belts!!! but it does work. Even using a wooden stick like a plumbers handle and prying around… put the end of the stethoscope on it and you’ll get noises transmitted. Just watch what you’re doing!!!


It would help if we could hear the sound. Tapping? Whining? Chattering? Have you eliminated the possibility that it could be an idler on a serpentine belt, or the water pump? The other stuff on belts (alternator, compressor, PS pump are not likely to fail at 112k, though the PS pump may whine a bit if the fluid is original.

Wandering idle is usually associated with an air or vacuum leak. I would pull all the intake tubing so you can get at the idle control valve and clean it. Look for cracks in all the air tubes and hoses. Let’s see, a 1999 could be either e36 or e46, depending on which 3-series model you have. If it is e36, clean the throttle body. If it is an e46, it is drive-by-wire so you can still clean the throttle body but you have to be really careful.

Does this car have an electric air pre-heater? Sometimes these whine and can make all kinds of weird sounds…right before they fail completely. once the engine is partially warmed up, they turn off. They don’t normally follow engine RPM, though. if it’s both electric, and powered by a belt, though…