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Is this normal? When the car is idling, the voltage coming off of the alternator measures between 11.xxV and 13.xxV as i cannot get exact numbers as they change quickly. As the engine is running, there is an audible pattern during the idle, like a small RPM change during idle and those numbers change along with the same audible pattern of the idle. Should this be a constant or no?
 

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Is this normal? When the car is idling, the voltage coming off of the alternator measures between 11.xxV and 13.xxV as i cannot get exact numbers as they change quickly. As the engine is running, there is an audible pattern during the idle, like a small RPM change during idle and those numbers change along with the same audible pattern of the idle. Should this be a constant or no?
I am guessing at this to some extent, however, many of the these cars have a special alternator pulley that is a one way clutch.

If the clutch seizes it can cause the alternator and serpentine belt to do strange things.

Watch the serpentine belt tensioner while the engine idles, if it appears to be walking back and forth then likely the alternator pulley is seized. The idler pulley/arm should be almost dead steady.
 

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I don't think any of the 2.0's use the alternator pulley clutches, at least the AEG doesn't. Has the alternator been replaced yet? It has enough miles on it now that the alternator or the brushes should have been replaced by now. You could just have worn brushes that starting to make intermittent contact now.
 

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It is possible the 2.0 does not have the one way alternator pulley, I do not deal with many 2.0 cars.

See picture below if the small black plastic cap that is on the front of the one way pulley. It may be possible that the pulley cover could fall off, it is doubtful. You could also check a parts application guide as well.
 

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Looks like a normal pulley to me. No clutch.

Things wear out over time. If the bearings are nice and smooth/quiet? I'd suggest just doing the repair kit and calling it a day.

S-
 

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Yet, its not a clutch pulley, even with the plastic cover missing, the clutch pulley does not have a visible nut.

Make sure the belt is not slipping, if the tensioner is good, then the problem is most likely the brushes/regulator which may be able to be replace from the outside of the alternator??

BMW alternators, or at least some of them have a brush/regulator module that can be replaced from the outside of the alternator.
 

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Discussion Starter #10
Could that voltage regulator be causing my problem in the other thread? Charging the battery but also shorting out and draining it as it sits?
 

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rough idle

My wife has a 2000 bug 2.0l automatic ,,,,well just like to say these post are very helpful so I have a Question for someone I am having an issue with my wifes bug when the alt is pluged in it shakes and idles real bad but when I unplug the alt and restar it if it didn't stall it out it will run smooth could this be the clutch thing happening
 

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Suggest you get the car to the parts store to have the charging system tested.

The alternator may have a bad diode and could be putting out too much AC ripple or the charging Voltage may be too high.

I do not believe the 2.0l had the AOP alternator clutch pulley, but you can see if it has a plastic cap on the end of the pulley like the picture I posted earlier in the thread.

You can also watch the belt and tensioner. The belt should be very stable at idle with little to no vibration or movement.
 

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regulator

Is this normal? When the car is idling, the voltage coming off of the alternator measures between 11.xxV and 13.xxV as i cannot get exact numbers as they change quickly. As the engine is running, there is an audible pattern during the idle, like a small RPM change during idle and those numbers change along with the same audible pattern of the idle. Should this be a constant or no?
Nope, the internal Regulator is suppose to keep a constant DC output. looks like the regulator inside the alternator is going bad. I would replace that first .
 
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