I fixed my surging problem with a reman amp from Ebay. A garage in California had ordered it for a customer who didn't show up for the work. I got it for $50. It wasn't the exact part number that the old one was, and the bracket didn't bolt to the car right(I used a wire-tie to hold it), but the connector connected. It works awesome. I tried the trick of re-soldering the points on the printed circuit of the old one before I bought this one, it didn't work. Plus, as soon as you open the case, the rebuilding companies don't want them anymore. One thing: make sure your linkages are set according to the factory manual and the pivot points are lubed with a little white lithium grease. It's too bad I didn't know you had this problem at the GTG, I would have taken out the actuator so you could have tried it in your car....process of elimination!! Just like the dealership techs do; "Substitute known good part!".

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83 M-B 300D- daily driver
83 240D gray market
2002 VW Jetta TDI- beater