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Discussion Starter #1 (Edited by Moderator)
I did not get many suggestions from this group, but I found out what my problem was and it was not electrical.
I had ask if there was a way to verify that a new MAF was bad. My car would go in to the default mode with the a new MAF after I reved it to 2700 RPM's and would stay in the default mode until I turned the ignition off. I would get a CEL and the fault would show improbable MAF reading.
The problem was caused by the intake pipe coming loose from the turbo suction. I had recently cleaned the intake manifold and had probably gotten oil on the turbo suction (there are no ridges on the aluminum pipe to hold the rubber coupling on). This plus the fact that the half circle clip that attaches the bracket to the plastic intake pipe was missing (did not know that it had one at the time). this allowed the rubber coupling to wiggle off of the turbo suction. There was not an air flow past the MAF, hence, no reading.
I glued the plastic bracket to the plastic intake pipe and also wrapped a brass wire around it. The car runs great now.
FYI, if you disconnect the MAF, a MK4 will go into the default mode from the gitgo. If the MAF is connected and the car only goes into the default mode after reaching 2600 to 3000 RPM I would suspect a leak between the turbo and the MAF. Now does anyone care to describe what the parameters of the default mode are? The "default mode" is not the same as the 'limp mode".
 

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Thanks for the update.

Not sure what value the ECU substitutes but when I disconnected a good MAF it feels like very low power. If you have VCDS, you could log what the ECU sees when the plug is disconnected.
 

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Discussion Starter #3
My car ran dramatically better with the MAF unplugged (default mode) than with the original bad MAF. In the default mode the ECU set the MAF at a constant 550 mg/str.
BTW, I am using the Pierburg MAF. I bought on Ebay for $78
 
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