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Discussion Starter #1 (Edited by Moderator)
I have a 2004 Jetta GLS TDI. I have been having a low power (limp mode?) issue for some time. It won't tach up past 3000 and sort of (not sure how to describe it) misses when it has to work hard such as going up hills or when I am accelerating. I had the fuel filter changed and ever since when I turn the key on I hear what sounds like the whine of an electric motor that seems to be coming from the engine compartment. You hear when driving also. My mechanic changed the fuel pump, the one located under the back seat, but that didn't solve the problem. He took it back out and put the old one in but the parts company would take it back so now I have a spare fuel pump to the tune of $340 My mechanic mentioned that my Jetta has two fuel pumps and I am wondering if the other one might be bad?
 

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Irscwab,
Is it throwing any error codes? (aka DTCs Diagnostic Trouble codes). For problems like this where it could be any number of things, it might be worth spending the money on a ross-tech VCDS, if you haven't already.

Dan
 

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Put your ear to the EGR valve and intake manifold flap and have a helper turn the key on and off. They are the things sticking out of the intake manifold. You will probably identify those as the things making the whining noise. If so, it's normal. They self calibrate and make tha tnoise when moving.

The limp mode has many possible causes, instead of chasing them down, get the car scanned for codes and see if anything is bad, then start tracing it. Take a look through this checklist for possible causes of low power. http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm If you're stuck anywhere or don't know something, please post a follow up.

Yes, the first fuel pump is in the fuel tank. It moves fuel up to the engine. The second fuel pump is on the end of the camshaft and moves fuel into the fuel rail inside the cylinder head.
 

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I have the same car with 165k miles on it. At about 130k it developed same symptoms. Turned out to be bad N75 valve. I'd check for vacuum issues first. Replacing the lift pump doesn't seem logical for these symptoms. Good information on this site and on Fred's TDI site. Maybe need a new mechanic.

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Low power TDI

I had exactly the same problem. Had the fuel filter replaced and the mechanic reversed the fuel lines. Another mechanic spotted the problem about 2 months later fixed the fuel line issue and ran like before.
 

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I have a 2007 VW Polo 1.9 TDI. I have the same issue when going up hills the car goes into limp mode. The codes say its the drive by wire. Is this problem simply solved by replacing the accelerator pedal?
 

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For what it's worth, if you do have a check engine light on and don't want to spring for a reader or VCDS, most auto parts stores will let you use an OBDII scanner for free in their parking lot. Before I purchased VCDS that's what I used to do. If you don't have any codes, you'll probably have to do some old fashioned home diagnosis. There are numerous things that can cause limp mode, so the aforementioned check list is a good place to start. Also, he N75 that the other user recommended is easy to check by swapping it with your N18 (an almost identical solenoid that actuated your anti-shudder valve) and checking if that fixes the problem. When I had a limp mode issue it ended up being that one of the connectors in my vac lines was clogged. I replaced all the lines but that wasn't the issue, so it took me a while to track down and ended up being solved almost accidentally when I deleted my EGR.
 
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