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I have an '03 Jetta TDI, and I have recently encountered a few (at this time seemingly minor) annoyances.

First, last week my car started surging (200 RPM) at constant speeds under 65 MPH. I have an auto-tranny (I know it has a bad reputation, so I expect some flak for that), and it only surges in 4th gear. No surging when I put it in 3rd gear and accelerate to 45-50 MPH. I was due for an oil change (not that I thought it would help, but it needed to be done), so a few days ago I changed my oil....which brings me to annoyance #2.

While under my car, I noticed oil on the back of my engine, turbo and actuator, and turbo pipe. Not a lot of oil, but definitely enough to get my attention. No oil on the top of the turbo, so it looks like it's the turbo oil return line instead of the supply line. I'm thinking (and hoping) it's just the gasket and not the line itself.

So now I have two things to fix, and some cleaning to do. The only solution that seems to apply to my surging problem is a faulty N75 valve. Found it on a diesel truck troubleshooting forum, but the guy who did the write-up called it a vacuum relay and said it also controlled the torque converter, which would cause the surge. Gonna replace my vacuum lines first, then the valve. I don't see the oil return hose failing (2/3 steel, 1/3 steel braid), but I know it's possible. Gaskets are cheap, so I'm going to replace that and hope for the best. I am also going to pull the manifold and clean it, since it's never been done.

I have read numerous posts that state limp mode is inevitable, and though I have yet to experience it, I fear it may be knocking on my door soon. I am debating on whether or not to replace the MAF and vane actuator while I have everything torn apart. Does this sound like a logical sequence of steps to take?
 

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I would not replace the MAF just for the heck of it. If you're going to throw money at it, buy a VCDS and at least you now have a tool to narrow the problem down. Same w/vane actuator. See the VNT actuator adjustment article in the FAQ, why replace a perfectly good part? So to answer your question, yes I would replace the vac lines on a 2003 due to age and mileage, no I wouldn't replace the other stuff unless you've tested it first.
 
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