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?

> 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.

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: , John G.Burns B.Eng, Bonny Scotland
Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html

Thank you. Can a dealer/mechanic test the sensor to see if it failing?


"John Burns" > wrote in message
...
> > 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.
>
> 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: , John G.Burns B.Eng, Bonny Scotland
> Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage!
> Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html

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, 40=B0F can't feel that cold. A lot of cars get stolen when
owners leave them idling that way.

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


"Michael Low" > wrote in message
ups.com...
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, 40°F can't feel that cold. A lot of cars get stolen when
owners leave them idling that way.

"Michael Low" > wrote in message
ups.com...
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

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.