Loss of turbo power around 3000-3400rpm

jeffbrom

Member
Joined
Feb 20, 2007
Location
Ohio
TDI
2002 Jetta tdi, auto
Hello All,
I have been trying to remedy this problem for some time. This is on a 2003 MKIV TDI with the auto transmission. If I accelerate at a brisk rate, such as 3/4 or full throttle, the turbo boost and acceleration is good till the rpms hit about 3000-3400 then power drops off, rpms drop off, and usually goes into limp mode with no boost at all and a CEL. Restart engine and repeat. If I let off the throttle, and vary the throttle position I can avoid the limp mode most times, but of course I am not accelerating like I should be!
I have tested and replaced the MAF with a known good from my 02 and still have the problem. I have checked and replaced the N-75 turbo boost solenoid valve, still have the problem. I had first tried NEW ones of both the above, but was unsure if they were defective, so did the swap with my known good ones to be sure.
I have a VAG-COM and have run the test for the turbo boost vacuum actuator and the linkage arm moves back and forth to the extent I would expect is full range, about 3/4-1". I have also disconnected the vacuum hose and used a handi-vac type hand pump and it moved the same.
Does anyone know of more tests I could perform to figure this out?
The car runs good otherwise, and doesn't burn any engine oil.
Some of my thoughts are that it could be carbon build-up cutting down air flow in the turbo? Maybe choked airflow in the intercooler area?
The engine in this car was swapped out with a good lower mileage engine before I purchased it 4 years ago, by a diesel mechanic who also did work on VW's, and I believe he said the intake was in good shape/clean before it was put in. The timing belt kit was done at that time also.
Any suggestions are appreciated, THANKS!
Jeff
 

super1

Veteran Member
Joined
Apr 19, 2010
Location
NY
TDI
none
Hello All,
I have been trying to remedy this problem for some time. This is on a 2003 MKIV TDI with the auto transmission. If I accelerate at a brisk rate, such as 3/4 or full throttle, the turbo boost and acceleration is good till the rpms hit about 3000-3400 then power drops off, rpms drop off, and usually goes into limp mode with no boost at all and a CEL. Restart engine and repeat. If I let off the throttle, and vary the throttle position I can avoid the limp mode most times, but of course I am not accelerating like I should be!
I have tested and replaced the MAF with a known good from my 02 and still have the problem. I have checked and replaced the N-75 turbo boost solenoid valve, still have the problem. I had first tried NEW ones of both the above, but was unsure if they were defective, so did the swap with my known good ones to be sure.
I have a VAG-COM and have run the test for the turbo boost vacuum actuator and the linkage arm moves back and forth to the extent I would expect is full range, about 3/4-1". I have also disconnected the vacuum hose and used a handi-vac type hand pump and it moved the same.
Does anyone know of more tests I could perform to figure this out?
The car runs good otherwise, and doesn't burn any engine oil.
Some of my thoughts are that it could be carbon build-up cutting down air flow in the turbo? Maybe choked airflow in the intercooler area?
The engine in this car was swapped out with a good lower mileage engine before I purchased it 4 years ago, by a diesel mechanic who also did work on VW's, and I believe he said the intake was in good shape/clean before it was put in. The timing belt kit was done at that time also.
Any suggestions are appreciated, THANKS!
Jeff


Did you take the clip off of the actuator arm to see if the turbo lever moves freely without any binding, also to see if the arm has full travel?
What kind of shape or your vacuum hoses in any leaks?


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Last edited:

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
Interweb guessing as well, I'm down at the turbo, specifically the actuator. Lots of other things it could be though.
Try the vacuum pump with a gauge on the actuator. It should just start to open at 3.5 to 5.0 "/Hg. Also observe how much to open all the way, iirc it's about 18(?). If it's close to but not in the 3.5 to 5 window, loosen the double nut, adjust the rod length until you get about 4. You can check if the vanes are frozen by operating the lever with your finger. If it's a bit sticky, exercise it, maybe even spray a little magic liquid on the vane area.
 

jeffbrom

Member
Joined
Feb 20, 2007
Location
Ohio
TDI
2002 Jetta tdi, auto
Thanks Super1 and BobnOH, The vacuum lines are new silicone lines, replaced them a while back when this problem started. They hold vacuum well. I also checked the vacuum pump, no leak at the outlet fittings. I will try your suggestions on the vacuum measurements and the disconnect of the linkage, etc. That info is much appreciated. It might be a few days before I can get to it. Thanks, have a nice weekend!
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
If you do remove the clip from the actuator rod, be warned, they get lost real easy. Use a magnet to catch it or a piece of tape or something so you can find it.
 

mgoff5000

Veteran Member
Joined
Aug 26, 2009
Location
Danville, CA
TDI
2000 Jetta, 2004 Passat (RIP)
Since you have vag-com you really want to log what’s going on as you drive. There’s a guide here or on MTD about troubleshooting boost issues. I wasted a bunch of time hoping it wasn’t crunchy vanes but it was. I learned the most by disconnecting the actuator and trying to manually move the vanes. As noted, just buy a spare clip ahead of time. Hardware stores will have as “c” or “e” clips I think. If it doesn’t move well there’s a great guide on taking it apart and cleaning. Just be prepared to wait a day or more for the PBlaster to get through the rust so you can open it.
 

jeffbrom

Member
Joined
Feb 20, 2007
Location
Ohio
TDI
2002 Jetta tdi, auto
Hello again,

Here is the code that is stored:

16618 - Boost Pressure Regulation PO234 - 35-10 - Limit Exceeded (Overboost Condition) - Intermittent

Please let me know where this leads as far as what to do or look at next.
Thanks,
Jeff
 

super1

Veteran Member
Joined
Apr 19, 2010
Location
NY
TDI
none
Hello again,

Here is the code that is stored:

16618 - Boost Pressure Regulation PO234 - 35-10 - Limit Exceeded (Overboost Condition) - Intermittent

Please let me know where this leads as far as what to do or look at next.
Thanks,
Jeff


I think you said you check the actuator? If it’s not binding take the clip off the actuator arm and see if the lever of Turbo arm has full range without binding


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Last edited:

joep1234

Veteran Member
Joined
Jan 2, 2014
Location
NC
TDI
former '04 Beetle TDI, now 2x '15 Audi Q5 TDI's, 2007 Dodge Ram 4x4 6.7
Also check your fuel filter. If it's stopped up, you will only get enough flow to support a certain rpm range.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Sounds like you need a turbo, unless you can get the mechanism freed up. While certainly possible, but not as likely, it could be the VNT's N75 not being able to vent vacuum properly and/or fast enough.
 
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