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RPM changes about 200-400 RPM while cruising between 40 and 65 MPH. Changed the valve body with a rebuitl one but did not help. There are no codes. Both the transmission shop and VW shop (Not a Dealer) can't figure it out. Any ideas out there. Car has about 133,000 miles. Fluid and filter changed.
The computer does show the TC slipping (locking and unlocking) but the trans shop does not beleive it is the TC, but someting telling it to do that.
Thanks in advance for any ideas.
 

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OK, let's assume it's not a transmission problem even though you've narrowed it down. Look through the low power FAQ article. There are many small things like vacuum line leaks or turbo/egr solenoid control problems that could cause similar problems.
 

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2001 Jetta surging

Thanks for the reply. We did put anothwer mass air sensor on to to see what would happen and it did not correct the problem. I'm going to go over as much as I can on the engine and see if I can figure this out. The car runs great, no problem with power,no smoking on acceleration, great mileage (38 in town) shifts great. Unless the the new valve body I installed is bad, I really think there is something with the engine ginving bad info to the computer.
 

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I know this thread is 6 months old, but if you haven't found the answer yet, I believe I found a link that will help you. I am having the exact same problem, but I do not have a CEL. I found a site for troubleshooting diesels (seems more truck-specific), but a similar problem listed there got my attention. It may be as simple as a leaking vacuum line or a faulty N75 valve. The article I found says the vacuum relay (which I believe to be the N75 valve on our cars) also affects the TC. Check it out.

http://flashoffroad.com/Diesel/troubleshoot/troubleshoot.htm

Jerking and Surging on a Turbo Diesel

One of the main causes is a bad injector pump. Many times their are multiple problems.

First thing I noticed was a jerking / surging/ bucking at around 2500 RPM on heavy acceleration or up steep grades while trying to maintain speed. Then the Engine Codes started to come up 1238 & 1247 (I think) They are Turbo Boost Pressure High & T B Press Low. I Figured I was loosing my TurboCharger or with any luck Just the Waste Gate.

With the cruise on and when I was going uphill the truck would lose power and puke black smoke and then the smoke would stop and I would have plenty of power again. This happened three or four times on one hill. Now remember these are Florida hills, not mountains. Another thing that I noticed was increased fuel consumption, went through about a tank (Main tank, not the aux.) in 160 miles.

This could be the vacuum relay failing. The solenoid controls the waste gate and the Torque Converter Lock/Unlock. The Bucking you get is the torque converter Locking & Unlocking at around 55 MPH And The Turbo Boost Press goes High and/or Low so you get Engine lights for High and Low Boost. This could also be a bad turbo or wastegate.

Turns out its the Vacuum Relay mounted on the Right Side Valve Cover. The Surging is the Torque Converter Locking On & Off because it can't decide where the vacuum is. After the vac relay was changed I have no more surging and no more Turbo Error Codes.
 

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I have a 2001 Golf TDI, rpm's are surging up & down also. In gear & out of gear. At idle. Did you find the cure for your surge problems.
 

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I have a 2001 Golf TDI, rpm's are surging up & down also. In gear & out of gear. At idle. Did you find the cure for your surge problems.
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You need to get your motor scanned (preferably with VAG-COM\VCDS) for any error codes logged in the ecu and post them, that will save a lot of guessing and check systems out.
 
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