I’ve got a 2006 Jetta TDi with just under 110,000 miles on the meter. The vehicle has had every service recommended by the manual religiously since we bought it new.
Recently, I’ve noticed a problem while driving on my daily commute. I travel Rt. 70 through Maryland on a daily basis, and there are a couple of decently steep stretches where you are climbing the side of a mountain.
While traveling at 65 and starting to head up the incline everything is just fine. Car is cruising along, no issues. But as I depress the pedal to maintain speed under the increased incline, just as the car would normally downshift from 6th to 5th gear, the entire car starts to buck.
It’s almost as if the car can’t decide if it wants to shift gears or not. Being a diesel, I don’t think its a misfire, but it kind of feels like that. Plus, if I let up on the pedal just a bit so that the car doesn’t want to shift, then it goes away almost instantly. I can put the engine under load, and as long as it doesn’t get to the point where the car would shift, it seems just fine.
This doesn’t happen with any other gear shift, 5 to 4, 4 to 3, or while shifting up from 4 to 5 or 5 to 6.
So, any ideas? I feel pretty certain it’s an transmission issue, but as to the specifics…well, thats why I’m asking you 
--Brian
I have more questions than answers:
–Is it a manual or automatic? I am not aware of a 6 speed auto–do you mean that the car is coming out of overdrive? Can you turn off the overdrive manually or manually downshift into fifth?
–I would recommend downshifting sooner manually–BEFORE you get to the steepest part of the hill. This way your engine RPMs are up and you have more power BEFORE you are putting the maximum load on the engine. Do this either by turning off the overdrive or manually downshifting if possible.
–Have you checked or changed the transmission fluid?
–Do you have a roof rack?
The car is a 6 speed auto (there was an option for a DSG Direct Shift Gearbox for that year with 6 speeds), there is no overdrive. It does have a “sports” feature where I can force it to downshift. I can give that a shot on my way home today and report the results.
The car had its 105k service about a month ago via the dealership. I assume that they checked the fluid and it was changes according to the manufacturers schedule as all of the recommended maintenance has been performed on the car. I will go out and verify fluid levels at lunch today and report results.
I have no roof rack.
I would suggest that you visit vwvortex.com. There are several forums there specifically targetted for VW owners. You might get better help over there. I have found very valuable information on my vehicles there. The other members are very helpful
Brobak would you mind posting what eventually happened with your Jetta TDI and how the issue turned out? Thanks.
I assume that they checked the fluid and it was changes according to the manufacturers schedule
This is one of the few things that I recommend something other than the factory maintenance. I would make sure the transmission fluid is changed like every 40,000 - 60,000 miles.
Good luck.