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Discussion Starter #1
Can someone pls advise me what an idler pulley is and what does it do ? and how would you know if it's faulty ??

thanks
 

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thanks Steve -

:confused:thanks Steve - now the idle part makes sense..... so would it for example have any effect on the revs or idling of the car or not ?? - soz - am very limited in mechanical knowledge of any sort.... am trying to establish if a faulty idle pulley is responsible for the high rev count - I only seem to notice it when going over 40mph and downhill - when i brake the revs shoot up to 2300 or thereabouts and stay there for at least a minute if not longer and only then does the car gear down....... just feels like i am chewing an aweful lot of fuel ........ or maybe it's just the way the automatic 200 cdi is.. I don;t know as I've nothing to complare it against - thanks
 

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Generally if an idler pulley goes faulty it's one of two things.

Firstly the bearing can go 'dry' causing the idler pulley to sound noisy or rough running rather than smooth. Alternatively the bearing can collapse causing the idler pulley to run off centre which will then tend to cause the other 'driven' pulleys to either chew up the drive belt or fling it off entirely.

Secondly the actual pulley itself can disintergrate which will then cause the belt to drop off or get tangled in other engine parts. Generally only plastic pulleys tend to do this.

I'm no expert on CDi's or automatics but I don't see any obvious connection between the symptoms you describe and an idler pulley. Why do you think the idler pulley is the cause of this?

Have you had the car tested for fault codes? I would think that it's far more likely to be a sensor (electrical) fault (mis-reading) rather than a mechanical fault. Generally with modern engines and automatic gearboxes all their behaviour tends to be determined by the Engine Management Unit which in turn depends on sensor readings to make it's decisions. Therfor if these are incorrect the car will behave in very strange ways.

Steve.
 

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:confused:thanks Steve - now the idle part makes sense..... so would it for example have any effect on the revs or idling of the car or not ?? - soz - am very limited in mechanical knowledge of any sort.... am trying to establish if a faulty idle pulley is responsible for the high rev count - I only seem to notice it when going over 40mph and downhill - when i brake the revs shoot up to 2300 or thereabouts and stay there for at least a minute if not longer and only then does the car gear down....... just feels like i am chewing an aweful lot of fuel ........ or maybe it's just the way the automatic 200 cdi is.. I don;t know as I've nothing to complare it against - thanks
What you are describing isn't about an IDLER, it's about the IDLE regulator. Idling is what engines do when you have your foot off the gas pedal and they are left to keep up their IDLE speed. An IDLER PULLEY keeps a drivebelt from hitting stuff, basically, and is quite unrelated to the Idle (speed) regulator.
 

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I didn't consider it being an idle regulator. Still I'm not sure this is possible, the car's a 200 CDi and as far as I know idle regulators are used on petrol engines as a bypass to the butterfly(s) to ensure that the engine doesn't stall when the throttle is closed and to stabilise rpm at idle.

I'm interested in the outcome of this and how idler pulleys have got dragged into the mix.

Steve.
 

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Discussion Starter #7
Steve hi

Clearly they are not related - was just an ignorant assumption on my part that the idle pulley had something to do with my seemingly high rev count. Anyway the pulley has now been replaced so thankfully the loud ticking noise has gone... and not sure if I'm imaging it or not but the revs don;t seem quite so high......... Am sure MB would have done all the checks and possibly adjusted something - anyway I am a happy bunny again - love my car it's just the best !
Regards
Aileen
 
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