528 Idle question

I own a 2000 528 with ~32000 miles. The other morning I started the car to let it warm abit. I noticed the car would idle and then the engine would
rev without any input from me. It would rev for a few seconds and then return to the pre-rev idle.
I have never noticed this as I start the car and go inside for a few minutes as the car warm. Is this normal?
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Oscillating idle can be the first sign of a failing O2 sensor. But they normally last a LOT longer than 32k miles.
--
Who needs a life when you've got Unix? :-)
Email: snipped-for-privacy@unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland
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Thank you. Can a dealer/mechanic test the sensor to see if it failing?
John G.Burns B.Eng, Bonny Scotland

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You shouldn't let the car idle for minutes unattended. It's bad for the car and the environment. The engine needs to warm up briskly so as to get into its normal efficient combustion mode. When the engine is cold it will burn a richer mixture and the excess unburnt fuel will collect on your catalytic converter (and slowly poison it $$$!) as well as into the environment. Idling a cold engine is bad practice.
The high revs may be due to idle input from the O2 sensors to the computer trying to warm up the engine so the exhaust isn't so "dirty". As the engine warms, the exhaust clears up enough to allow the idle go back to "normal". But the exhaust from idling is always going to be dirty because the catalytic converter won't be hot enough to scrub the exhaust "clean".
If you read the BMW car manual it says to start the car and then just drive off at a moderate pace until the engine is at its normal temperature. Then you can press the engine harder if you want to.
Anyway, 40F can't feel that cold. A lot of cars get stolen when owners leave them idling that way.
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WOW!
Thanks for the insight.
I have an 1966 Sting Ray and I know too much idling cause the engine to run poorly. So I guess the same must be true for even modern machines.
Again, thank you.
Alan
You shouldn't let the car idle for minutes unattended. It's bad for the car and the environment. The engine needs to warm up briskly so as to get into its normal efficient combustion mode. When the engine is cold it will burn a richer mixture and the excess unburnt fuel will collect on your catalytic converter (and slowly poison it $$$!) as well as into the environment. Idling a cold engine is bad practice.
The high revs may be due to idle input from the O2 sensors to the computer trying to warm up the engine so the exhaust isn't so "dirty". As the engine warms, the exhaust clears up enough to allow the idle go back to "normal". But the exhaust from idling is always going to be dirty because the catalytic converter won't be hot enough to scrub the exhaust "clean".
If you read the BMW car manual it says to start the car and then just drive off at a moderate pace until the engine is at its normal temperature. Then you can press the engine harder if you want to.
Anyway, 40F can't feel that cold. A lot of cars get stolen when owners leave them idling that way.
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You're welcome. Carbon deposits from unburnt fuel can come from a number of sources including too much idling. The deposits can cause a downward spiraling effect.
The cold start mechanism is like a kludge running mode that your car needs to get out of as soon as possible. Everything is best protected when the engine is working at specified temperatures. You'll also notice improved gas mileage.
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You shouldn't let the car idle for minutes unattended. It's bad for the car and the environment. The engine needs to warm up briskly so as to get into its normal efficient combustion mode. When the engine is cold it will burn a richer mixture and the excess unburnt fuel will collect on your catalytic converter (and slowly poison it $$$!) as well as into the environment. Idling a cold engine is bad practice.
I agree. The one time I attempted to idle my 328i (in about 5" of snow), the heater would not cooperate & blew only cold air until the car was moved.
Tom
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