124 300te 4matic Revs at idle ?

[brucemillar]

Hi

My W124 at idle has a rather soothing rythmic reving pattern. About every 15 - 20 seconds the revs rise very slightly. This is hardly registered on the rev counter but does show on the oil pressure gauge.

I have no idea if this normal?

I have cleaned the throttle body (very little muck in there)
Replaced the air filter (wasn't too shabby)

As part of a general clean up I also cleaned (contacts) and replaced all of the fuses.

Any help / clues appreciated.

 

[grober]

Sounds like what is often described as "hunting at idle" This sometimes cause by an incorrect fuel mixture. Could be a slightly dodgy Lambda sensor or slightly rich mixture- best adjusted with an exhaust gas analyser measuring C02 level.Other possibility is a sticky motorised idle control valve[ if its got one?]- its fed from the OVP relay so slightly dodgy relay pins or internal contacts might be to blame?

 

[brucemillar]

Grober

Thank you. It is a very light hunting. Would you happen to know where I would find the OVP relay?

Bruce

 

[carat 3.6]

Grober

Thank you. It is a very light hunting. Would you happen to know where I would find the OVP relay?

Bruce

The ovp relay is behind the battery , under ther plastic shroud.

 

[brucemillar]

Thank you. I shall have a look see.

 

[ray_hennig]

Yep!

Grober

Thank you. It is a very light hunting. Would you happen to know where I would find the OVP relay?

Bruce

I would go with Grober on that but also suggest a vacuum leak. Worth checking hoses around the idle control valve and any little 'boots' (is that right?) that connect vacuum hoses to anything. Also the ICV itself as their open/shut performance degrades over the years.

OVP relay, as has been said, is behind the battery but I doubt that failure symptoms would be as mild as 'light hunting'.

Bonne chance.

RayH

 

[brucemillar]

Good stuff.

I will spray the hoses with some damp start and have a look at the ICV.


Thanks.

Bruce

 

[brucemillar]

Progress

I found that a sensor on the intake just ahead of the air box was floating around. The gasket had disintegrated. Replaced with a home made washer. Revs seem much steadier. I also sprayed hoses with damp start with no effect. Had a look at the OVP. It looked brand new. Assuming it is the one with two 10 amp fuses?

Thanks again

Bruce