Moaning sound from engine at idle.

[atomicveilside]

Hi everyone,

I have a strange moaning sound that comes from the engine compartment at idle. I drive 12 miles to work every day. I get in the car and start it and there's no moaning sound. Drive away to work for the first half of the journey every time I come to traffic lights or stop the car starts to idle then comes this strange moaning sound, it lasts for about 1 second then goes away and can happen multiple times at one set of lights. I have noticed that the revs of the engine change slightly when this happens almost like somthing is switching on.. by the time I get to work the noise has stopped it then wont do it untill the next mornings journey. It's just been into Porsche for £3.000 worth of service and repairs but they couldnt find anything at all wrong. I've heared of things making a vacuam cleaner noise/ whine but not this sort of moaning sound. The cars away in the garage for winter and I would like to try and sort it out if i can. it's been doing it for about 4 months now..

Anyone every had or heared of this?

Cheers

A

[jpflip]

I remember reading something similar and finally found it on 6speed mooing sound...

[Loren]

Usually that sound is one of the diverter valves.

In a few rare cases I have seen it be a bad or loose hose but that is usually more prevalent at wide open throttle.

[atomicveilside]

I'm too sure if it is the diverter valves. the link above on 6 speed someone says it could be the power assist pump. i've checked the fluid level and all seams ok. and i would have thought if it was the diverter valves it would o it all the time and not just when cold.. hmmm is there a valve that control the emmisions? as i was thinking it could be that making the noise..

[wvicary]

Does operating the A/C compressor make any change?

[RFM]

If the car is equipped with a manual transmission, when the noise is present, push in the clutch pedal and check if the noise is still present or go's away.