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Discussion Starter #1
I have a 2.0 2000 GL Beetle and I'm getting the code P1129 from what I believe is the Mass Air Flow Sensor. There are no other codes being generated, so if the problem is not the MAF Sensor, the only other thing I can think of is the air pump. From what I've read the air pump only runs when the engine is cold, or below normal operating temperature. Because there are no other codes I'm at a loss as to where to look for the problem. Anyone have any experience or ideas? Thanks!
 

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RARELY do engines run rich, many times these are false indicators.

However, on the 2.0l, check the fuel pressure regulator first and make sure it is not broken/leaking.

If you can get Freeze Frame data for the code as well as see what the Long Term Fuel Trim is at both idle and steady cruise in the 45-55 MPH range.

Also verify engine coolant temp, should be around 205F at idle.

MAF being dirty causes lean conditions typically, so I would not worry about trying to clean it at this point.
 

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Discussion Starter #4
I cleaned MAF and cleared the code, then about 8-10 days later the code re-appeared, so I replaced the MAF 7 days ago and the check engine light has not reset itself.
 

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With the exception of stuck/leaking purge systems, most cars and trunks could not likely ever run rich.

Most things degrade with age and mileage, fuel filters get restricted, fuel pumps loose pressure, MAF's under report, O2 sensors usually get lazy and do not switch fast enough, injectors would more likely get clogged than leak, very few issues cause rich conditions.

Usually when I find a car with negative (-) fuel trims or rich codes, the first thing I do is expect a false reading from a sensor, but I still check the basics as well.

It is just common sense and history that the majority of fuel control problems fail lean and not rich. I would guess less than 10% of all fuel control problems fall into a rich situaiton.
 
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