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I have a 2005 VW Jetta TDI that has around 120K miles and auto trans and otherwise runs great. Just recently it has started "hunting" between 4th & 5th gear while the cruise is engaged, depending on the load, but so bad you have to force the trans into 5th to keep it from going back & forth. First dealer said there were no error codes, but that I had a leaky intake boost hose and I needed to change my fuel filter. I changed the fuel filter, didnt have time to change the hose, and went to a second dealer. This dealer said, "no, the fuel filter and hose wouldnt have caused the problem". They said that the EGR valve was definately bad, and that also the throttle body either needed changing or at least a good cleaning (but they couldnt clean it for some reason). Then took the car to a local non-dealer shop with a mechanic that was suppose to be very good with the VWs/Audis (he may be - dont know). Told them everything that has transpired. They stated that after looking at the EGR/throttle body, that those 2 were definately not the culprits. I had them go ahead and change the EGR and intake hose and clean the throttle body. He didnt really know what to do at this point but stated it seemed that the engine was losing power, causing the cruise to hunt. I had to use the vehicle at this point but still does it. Where do I go from here to find the problem? Again, there were no error codes. Compression? Boost tests? Any help greatly appreciated.
 

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So the dealer sent you to an independent shop that is good with VW/Audi? Is it a VW dealer or a Ford dealer?

Compression could be an issue but without more tests, it's a guess. You can try a boost leak test. My guess: wiring, sensor, injector, or timing problem.

Is it on the original timing belt? Change interval is 100k. The timing could have severely drifted. Could it be related to the automatic transmission? Maybe since you're locking it in 5th and it seems fine otherwise. Check out the limp mode FAQ article, there are many possible causes of low power. However, it doesn't sounds like you are having low power, it's just with the cruise control engaged?

Is this an older square headlight mk4 2005 Jetta or the newer round headlight mk5 2005.5 Jetta?
 

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No, the dealer didnt send me or recommend the shop. Where I live (West Monroe, LA) there are no VW dealers so I have to do the best I can at getting service, and so far this one shop seems to have done the best job in the past, but they are stumped on this one (just like 2 large dealerships). I'm sure its a case of just finding the right expertese. I went to the dealers because I was in training in Houston and visiting family in S. Texas.

I will pass on your suggestions when I get back in country (I'm out of the country right now so can't deal w/ the car).

No the timing belt was changed just after it rolled over 100K. It certainly didnt start immediately after it was changed, and I now remember it sometimes doing it on steeper inclines before I had it changed. It just recently (within the past 2 months) became very noticable and basically unusable.

It doesn't FEEL like low power either, but noone I've taken it to has honed in on the cruise or AT at this point.

I'm guessing its the older MK4 since it has the square headlights.

I'm an A, B, C kind of problem solver, so just looking for some recommendations forward in order of priority: 1) compression test, boost leak test, take the transmission to an AT specialist?? Any concrete directions or suggestions or know where to get some expert help from VW engineers?

Thanks.
 
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