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My uncles R had a little problem over the last couple of days but he's being a bit vague. Its a 2008 with 43800 miles and for whatever reason he got the engine sensors changed because it started to idle at 1000 rpm. 200 miles later the car is doing it again but the engine light came on. He took it back to his VW specialist again and the car idled fine when he got there and they did a diagnostic and no codes got chucked up? But for now its running fine. Any reason? I said to get the guy to check the MAF and lamda's
 

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Dear Unc needs to be a bit more specific. There are 5 or 6 engine specific sensors, plus the throttle and pedal.

Failing over to a fixed rpm could be a sign of intermittant pedal / throttle pot failure. There are 2 variable resistors (aka 'pot' or potentiometer) in the throttle and 2 in the pedal and all 4 have to agree (within an allowed small tolerance), which forms the safety check. If there's a problem there, the ECU opens the throttle a fixed amount for the 'limp home' function. The simple test there would be to press the throttle with the engine running, if the revs don't increase, the ECU doesn't like the pedal.

I've never heard of MK5 throttle going bad, but I have heard of the floor mounted flavour of pedals causing problems.
 

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Greetings to All,

Sounds as though we on this side of the pond (the left coast of the Colonies) have a similar problem. Forums out here note the same issue, but none to my knowledge have posted the definitive answer to the issue. I have read the following: battery cells going bad, battery acid cooked out by heat. I checked my cell fluid - Ok, ran a load test on the battery and it was ok. Alternator is beginning to fail so the RPM compensates for low voltage/amperage, so I ran a test on the alternator and it was OK.

Some have offered that the MAF is 1)Failing, or 2)Dirty, so either clean or replace. Oh, like we're all made of money and will just replace one to see whether that works. Checking for dirt/grease/oil on my MAF is next on my list.

My local mechanic, a bright fellow, still has no idea what is behind the odd idle.

This happens in cool weather. Cool and rainy weather. Clear and warm weather. Hot weather. It makes no difference, it appears that the weather conditions have no effect upon the odd idle.

I am more than open to suggestions as to a resolution.

My best,
Doc Powell
 
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