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Q: Hi, I have an intermittent fault, when I drop down the gears, occasionally, the acceleration becomes sluggish, and car vibrates.

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I find that when I move down in gears when I come to accelerate again, the car becomes very sluggish and vibrates as if going over rumble strips. Also, the engine sounds rough. When I turn the ignition off and on again, I find that the problem goes away, but comes back again at various times. I have, today, changed the air filter as I was advised to do so. This seemed to improve things for a short time, however, I have just been out in the car again and the problem is still happening. Thank you in advance

My car has 102000 miles.
My car has a manual transmission.

A common problem with the 1.9L diesel motor is injector timing. Injector timing is critical and can have many varied symptoms. At 102,000 miles, I have to wonder if the timing belt has been done. The timing belt is what drives the diesel fuel injection pump. This pump both injects fuel into the cylinders and times when this occurs. Much in the same way spark timing is times on a gas powered vehicle. If the timing belt is stretching, it can affect diesel injection timing. If a timing belt has been done recently, I would suspect the injection timing will need to be adjusted.

Injector timing has a range it can be set in. If timing falls to one end or the other of the spectrum, it can have interesting drivability symptoms depending on the climate you live in. Cold start issues and excessive black smoke out the tailpipe are some other symptoms of less than optimal injection timing. These symptoms are unique to the 1.9L VW diesel motor.

Another issue that occurs with the 1.9l are clogged intake passages. Usually this is discovered when the owner finds they don’t have enough power to drive on the highway. The intake passages can clog with carbon in a number of passages in the intake manifold. This is a factor of the EGR system. Carbon will literally condense as it exits the hot exhaust into the colder intake manifold. The EGR cooler is particularly prone to clogging in this way.

These are the most common issues I have seen with the 1.9l VW diesel motor, but there are more. It will take an experienced VW technician to decipher what is what on your vehicle. I recommend calling our customer service line to see if there are any experienced VW technicians in your area to diagnose your acceleration issue.

Good luck!

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