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Discussion Starter #1
Hey all, I bought a 2001 Jetta TDI 5-speed manual back in November. Only mod to the car is an Upsolute chip installed by the previous owner. The car ran great, with no major issues. Then I decided to clean the intake manifold. Things were great, then about a week after cleaning, I began having issues with limp mode.

Now I'm getting limp mode accompanied by a P1556 Negative Pressure Deviation code when pulling a hill at 2k-2.5k RPM in 4th or 5th gear, and only part throttle. I can pull a hill with the "pedal to the medal" just fine, turn around and hit the same hill at part throttle and get limp mode. One of the common causes are vacuum leaks, so I checked the vacuum lines. After checking the vacuum lines no less than a dozen times, I can confirm they are all connected and routed in the proper configuration. Since I didn't haven't this issue before the cleaning, I assume that none of the hoses have holes.

I rented a hand vacuum pump from Advance Auto to try to actuate the VNT actuator. I found that the actuator does move, but will only hold 15 inHg vacuum. I'm not sure if this was the pump hitting its limit, or actuator leaking.

So, I might have a bad actuator. Since the actuator moves, does that mean that my VNT vanes are alright, or is it possible they are frozen as well?

Where can I get the circlip for the actuator lever without having to buy the whole actuator?

Is it possible that the newly cleaned intake manifold has caused this problem to surface, or is it just coincidence?

Thanks for your input.
 

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Where can I get the circlip for the actuator lever without having to buy the whole actuator?
1/4" "E" clip... Old-time hardware stores (are there any left???) should have this... when I was looking for one, the folks at Home Depot had never heard of this... Harbor Freight may have a kit of a zillion E-Clips of multiple sizes...

Yuri
 

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One of the common causes are vacuum leaks, so I checked the vacuum lines. After checking the vacuum lines no less than a dozen times, I can confirm they are all connected and routed in the proper configuration. Since I didn't haven't this issue before the cleaning, I assume that none of the hoses have holes.

I rented a hand vacuum pump from Advance Auto to try to actuate the VNT actuator. I found that the actuator does move, but will only hold 15 inHg vacuum. I'm not sure if this was the pump hitting its limit, or actuator leaking.

So, I might have a bad actuator. Since the actuator moves, does that mean that my VNT vanes are alright, or is it possible they are frozen as well?

Where can I get the circlip for the actuator lever without having to buy the whole actuator?

Is it possible that the newly cleaned intake manifold has caused this problem to surface, or is it just coincidence?

Thanks for your input.
It's possible moving, pulling, hoses could have cracked one of them. They're braided so unless you pressure test them you don't really know if they're intact. Normally the braids fray but you could have a crack in the middle or crack at the end of one of the hoses.

If you ran a known good vacuum line to the can to isolate the problem to the lines or can and found that it's not holding pressure, you found the problem, assuming it's not a problem with the hand pump. Try blocking the hand pump and see how much vac it can hold to make sure it's not the hand pump. If vanes are stuck the can will still hold vac, it just won't move.
 

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Hi Laceface welcometomyturbodies

I would just buy a length of the vacuum hose and replace the lot, like Chitty says you can't tell if they're leaking or not without testing them but I found the tubing to be that cheap I just replaced the whole lot one section at a time and it certainly rules the vacuum pipes out.:)
 

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Discussion Starter #5
Just realized that I goofed on my username. I'm Laserface (with an R) on every other forum on which I have registered.

The actuator rod moves just fine, so I believe the VNT vanes aren't stuck. I'll try to find a reliable vacuum pump to test with and focus on the vacuum lines. But it may simply be easier to replace the 175k mile/10 year old lines like Seatman suggests.

Thanks for your input guys.
 

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Discussion Starter #6
I got the vacuum lines switched out today. Took it for a drive, and no limp mode! I tried my best to vary engine speed and load to produce limp mode, but I couldn't find it. I'm worried that I didn't push its "buttons" right to hit limp mode. I'm going to borrow a vacuum pump tomorrow just to make sure the VNT actuator will hold more than 15 inHg.
 

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Discussion Starter #9
So I couldn't get the vacuum pump on Saturday (Feb. 19). The car was parked Saturday evening and Sunday because the big vacuum line to the brake booster split (no brakes!). Got that fixed, and in my first 5 miles of driving on Monday (Feb. 21) I hit limp mode twice. Both times I pulled over and restarted the car. After the second restart, the car did fine and has done great for the 500+ miles I drove this week.

My theory: Bad vacuum line causing the VNT actuator to not open/close all the way, causing a sticky spot in the vanes, and limp mode. Replaced the vacuum lines, but the sticky spot remained, causing limp mode. I started driving the car harder (because I was getting limp mode at part throttle) and the vanes broke free. Its theory, but it sounds good.

For anyone reading this with limp mode, CHECK YOUR VACUUM LINES. Even if they "look" good. Mine looked fine, but when I began removing them, over half fell to pieces in my hands.

Thanks guys.
 

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first post.i've struggled with this issue for ever. swapped turbos,changed vacum lines, new solenoids and so on and on. I've ordered a new actuator as it looks done,jerky movement etc and i hope this finally fixes it. i'll let you all know.
 

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...I hit limp mode twice. Both times I pulled over and restarted the car.
It's possible (with a manual transmission) to leave the car in gear, turn off the ignition for a second (as long as it's safe given traffic and a straight road with no need to turn the wheel - in case the interlock engages) and turn it back on...

I think this technique should be highlighted in the Owners' Manual so that TDI owners can be prepared ahead of time...

Yuri
 

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Discussion Starter #13
I still have this issue even after replacing all the vacuum hoses. Actuator does move as well..
The key to further troubleshooting is knowing if the car is overboosting or underboosting (caused by different things). It will narrow down the search. The guide/how-to on this site is enormously helpful.
 

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Discussion Starter #14
After several days of hard rain last week, my limp mode came back (the car has no bellypan/undercover, I suspect the water finished off the actuator). The turbo also seems really laggy when the engine is cold, and that's when it gets limp mode the worst. I finally got a vacuum pump to test the actuator. The pump will only hold 15 inhg, but the actuator is not releasing smoothly, but rather jumpily and with a distinctive pop (you can actually hear it move up and down). I cannot visually see the actuator release, but it sounds and feels like the bad actuator in the video about testing an actuator. I'm going to go ahead and order a new actuator along with a skid plate to cover the underside of the engine.
 
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