Intermittent, but consistent, limp mode at highway speeds

Hi Folks,

I have a question about the "symptoms" my 03 Jetta TDI is currently experiencing. I've looked through the forums and identified some of the things that could be kicking my car into limp mode at highway speeds. I've ruled out mechanical failure of the turbo, because boost is lost only intermittently, and turning the car off and then on again fixes the issue if only temporarily. However, there are a set of conditions that consistently will put the car into limp mode:

• It does not occur in gears 1-3, regardless of RPMs or speed.
• In 4th gear, the car will consistently go into limp mode at 3500-3750 RPM, most predictably when the engine is not fully warmed up.
• A CEL light for "Overboost Condition" will sometimes be triggered (but sometimes it won't).
  • The CEL may turn itself off or I may have to clear it myself. I've had it happen both ways.
• Turning the car off and turning it back on will resolve the issue. It may fix it for the remainder of the trip, or it may drop back into limp mode in 5th gear at around 70-80mph if on the highway.

My gut says it's the N75, but I would appreciate any suggestions from the folks on the forum. Currently the weather is in the single digits here in Maine and I have newborn triplets at home, so if I could get some suggestions on where to start or what it most likely may be, it would help to make my diagnostic work more effective (and keep the wife, who will be watching the triplets, much happier ).


Thanks!

Could possibly be your turbo actuator or sticking turbo vanes. Check to see if your actuator is moving within its full range and maybe do the EasyOff Oven Cleaner turbo clean to free up the vanes.

Okay, so I did some more research, grabbed myself some vacuum hose and a Mityvac, and went to work:

• All vacuum hoses have been replaced - no dice.
• Vacuum system is pulling -25"Hg, which is where it should be from what I understand.
• The actuator does NOT hold vacuum - I would draw back to -25"Hg and it would slowly lose vacuum until it returned to 0.
• THE BIG ONE - The turbo actuator lever is stuck and does not budge.

So what is my next move? If it were either the actuator OR the dirty turbo, I could take care of it with everything still on the car by swapping the actuator or hitting the turbo with oven cleaner. However, it seems as though both the actuator is bad AND the turbo needs to be disassembled and cleaned.

I take it that at this point, it makes the most sense to just pull the turbo and get the job done, right? How does this compare to a timing belt change? I've done two of those - time consuming, but not incredibly hard. I figure if I dedicate a weekend to it, I should be able to pull it off. Any tips or suggestions?

Or, better question: Is the actuator actually bad? Should it hold the vacuum firm?

Update:

The actuator is actually stuck solid. Would this be caused by corrosion from salt or what? Anyway, the lever on the turbo actually wiggles a small amount, but the actuator rod doesn't move at all. I'm hoping replacing the actuator will fix it enough that I can blow the crud out of the turbo with a nice Italian tune up.

I was experiencing the same issue with the limp mode. I tried the easy off oven cleaner. Worked for a very short time. I ended up taking the turbo off and taking the thing apart. It was stuburn to come apart. I ended up reading that someone on here put their turbo on the grill after he cooked steaks. Well when I read that I was in the middle of grilling. It worked like a charm gilled at 500 for 20 min. Then when it was apart and hot still I sprayed ez off cleaner on it. Worked great.

iMac6 said:

The actuator is actually stuck solid. Would this be caused by corrosion from salt or what? Anyway, the lever on the turbo actually wiggles a small amount, but the actuator rod doesn't move at all. I'm hoping replacing the actuator will fix it enough that I can blow the crud out of the turbo with a nice Italian tune up.

Click to expand...

When you replace the actuator there will be a hole in the side of it.
That hole is supposed to face the heat shield and the hot (exhaust) side of the turbo.

And yes, it should hold vacuum, but that doesn't matter much now that you found it to be stuck entirely. Either symptom would lead you to same replacement.

CopaMundial said:

And yes, it should hold vacuum, but that doesn't matter much now that you found it to be stuck entirely. Either symptom would lead you to same replacement.

Click to expand...

Thanks for the tip! I'm hoping that I find a nice, smooth, free VNT once I get in there.

SUCCESS! The actuator was locked right up, but the turbo itself moved freely. Put the new actuator on and took it out for an Italian tune-up. It's like I have a brand new car!