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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old November 11th, 2005, 14:29   #1
Join Date: Oct 2005
Location: California
Default Engine Overboost

I have a 2002 VW TDI New Beetle, purchased used with approximately 65,000 miles on it. It currently has 84,000 miles. In mid July 2005 I began experiencing a loss of power at higher speeds (70mph+). I was told the fuel filter might be clogged and I replaced the filter. This did not work. Over the course of about a week it continued to get worse and the check engine light came on. By now the car had reduced power at lower speed also. A co-worker had access to a generic scan tool and we checked the
error code. The code was "P234 " which indicated an engine overboost condition. I took the car to a local German car "Specialist", German Auto, in San Luis Obispo. They kept the car for about 3 weeks, charged me $500
and when I got the car it drove fine for about 50 miles. Shortly thereafter, the check engine light came back on (same code) and the car was one again experiencing a loss of power (in limp mode).

For the $500 the German Auto folks changed the mass air flow sensor, vacuum pipe and coverter. Needless to say I was quite unhappy and went back to them. They refused to give me my money back and said that they would continue to try and diagnose the problem. Their next proposal was to clean the air intake manifold of carbon build-up for $400. In the course of the conversation it became apparent to me that the mechanic really didn't understand much about how the diesel engine worked, this was confirmed when he said that a diesel engine does not produce NOx (nitrogen oxide)
emissions. Another somewhat puzzling point was that it appears after the check engine code is cleared the car runs ok for a short time 30 - 50 miles (even when accelerating quickly and at high speeds, two conditions which
seem to trigger the error message and send the car into limp mode). It seems that if the air intake manifold was truly plugged that clearing the check engine code would not result in proper operation, even for short durations. I am going to take the car to the local VW dealer but don't
have high expectations for success there either.

Has anyone encountered this code "P234 engine overboost condition" ? Any help or suggestions would be greatly appreciated.
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Old November 11th, 2005, 16:04   #2
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Join Date: May 2001
Location: Dorchester
Default Re: Engine Overboost

Engine overboost:Actuator rod rusty, inspect rod for rust and scaling .Physically try moving the rod,push down on the lever to which it is attached,it should move about 3/8 inch,if not remove actuator and see if the lever moves freely ,if not there is a problem internally with the vane mechanism which would require replacement of the turbo.
This is not an unusual problem ,I see this alot at the dealership at which work at.
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Old November 11th, 2005, 21:22   #3
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pghPAtdi's Avatar
Join Date: Mar 2003
Location: Nova Scotia to Pittsburgh and back
Fuel Economy: 57/40/34
Default Re: Engine Overboost

I too have been gettin the pos deviation for some time. My issue lies inside the turbo, sticking vanes. On the other hand my boss was having issues, he swapped in a new turbo to fix his problem. He took the old one home and thought to spray some penetrating fluid into the vacuum actuator which hangs off the backside of the turbo. Moments later her heard a "POP" and the action now freely moves up and down.

So, jack that thing up (jack stands or rhino ramps) and check out the movement on that rod. Spray some penetrating fluid on the livkage and into the topside of the gold colored can where the rod goes in and work it up and down . Who Knows, maybe......

basically what the dazzler said

Good luck
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