Engine noise when idling

[Laurent996]

Hi,

For a few months I noticed the following. When my car is idling after driving for 5to 15 minutes (usually when stopped at a traffic light), I almost always hear a noise coming from the engine bay that sounds like the air pump that runs for a minute when the engine is cold. This only lasts for one or two seconds, so I never had a chance to take a closer look at see if it's actually the air pump or something else. Also, this is happening the first time I stop, but not every time. It doesn't seem related to engine temperature as I saw it happening when the engine is cold as well as beyond 180 degrees. I also noticed that both RPM and voltage go down a little for an instant when this happens. The AC is off so I rule this out.

Does anyone have a clue about why this is happening now? I don't have any fault code, so I suppose this is not a serious issue, but I'd be glad to have an explanation.

TIA.

Laurent

[ohberlin]

Laurent, just wondering if your heat is on at the time.

[Laurent996]

Hi Ohberlin,

Currently, yes, but I don't see that as a symptom: it was already happening last summer with temps in excess of 90 degrees.

[1999Porsche911]

Is your engine compartment fan kicking on?

[Malakas]

This is happening to me as well... 2002 C4S with 45K miles.

The air pump (saw like) sounds comes on when I start the car in the morning, but now is coming on intermittently and much more frequently. I will turn the heater to 60 and see if it still occurs... its starting to concern me.

All thoughts welcome!

[Malakas]

... update. So it does seem to happen less if the heater is off.

[RFM]

I have no idea what the outside temperature is in Houston, but from + 4 C° and hotter, the airco compressor is working with the heater ON, if you switch the heater OFF the compressor is OFF as well. There is a chance that you hear the compressor running with too LITTLE R134a ( gas ) in the system, let check the system for a leak and the capacity. ( 850 gramme is needed )

[kidsmurf2000]

I had something similar, not exactly the same... there was a noise from the engine at idle, and the engine would rev with the noise. It cycled every 5-10 seconds at idle, though it would come and go.

That problem was fixed by a new ignition under warranty... I'm guessing around 75k miles.