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Old October 7th, 2019, 10:02   #1
UncleSpence
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Join Date: Aug 2015
Location: Bryan, TX
TDI(s): 2003 Jetta
Fuel Economy: 38-44mpg
Default Limp Mode and Warm Starting Issues

So I've done a bunch of back digging and found quite a few older threads that rarely get resolved, or at least never report back the solution, and haven't stumbled on the right thread yet, so anyone is welcome to point me in that direction as well.

First problem is the limp mode. Car has been prone to limp mode for the past 3 years or so. It was pretty rare for a long while. Would only happen on long trips and if I really was pushing it hard (car is automatic with 130k). Restarting the car always resolved it. Limp mode started to get more prominent, so I decided to make a stab at resolving it while doing some preventative maintenance. I did a timing belt as well as fuel filter change at around 128k and cleaned out the intake, replaced all my vacuum hoses, and put on a new MAF sesnor. Car started rough after timing belt, but with VAGCOM and changing the injection pump timing it ran as smooth as is ever had.
Limp mode was more prominent after this and would pretty much always go into it when driving at any intensity. I went ahead and replaced the EGR valve based on the new engine fault codes it was telling me with VAGCOM. Didn't help... At all. So the last thing I could consider as based on previous experience was the N75 valve. Replaced that, and chemically cleaned the turbo actuator and did the whole vacuum pump testing. It would move before, but moved much better and more freely after the cleaning. Now its back to its old self. Still going into limp mode, but less frequently. Randomly when I am going up a subtle hill or leaving a stop light. Engine light is intermittent and tells me that there's overboosting of the turbo.

All this has taken place over the past 2-3 months with much research throughout.

Second problem fastforward to now. Saturday, car is parked at a friends for a few hours. I go to leave and it doesn't just fire right up. Starter cranks for 3-5 seconds and then starts. Runs normal. Two days later I'm going through a small village in Texas after driving for a few hours, stop at a light, it goes into limp mode, I go into neutral turn off the car (to reset computer) and car won't start. I pull over wait ten minutes while searching the forum, car won't start. Luckily I had stopped near a semi yard with some mechanics that had come in early to drink coffee and shoot the breeze. They gave me a little gasoline and a rag to put in the intake to get it started again and to drive home. I get home 40 minutes later, turn the car off, engage ignition, and it fires up like no problem at all. Seems like an intermittent fuel/electrical-fuel problem. Open to theories that doesn't require me blindly throwing parts at it like the limp mode suggestions.
Really wished my car was manual as I was rolling to a stop.

Thanks in advance.
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Old October 7th, 2019, 10:15   #2
UncleSpence
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TDI(s): 2003 Jetta
Fuel Economy: 38-44mpg
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Additional anecdote, I was trying to do the unplug the temperature sensor that is below the vacuum pump at the rear of the head, but when I'd start to pull on the plug, coolant would start to drip, and I was afraid of causing a gusher that I wasn't prepared to handle. I just needed the car to start, which is why I enlisted the help of petro.
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Old October 7th, 2019, 19:16   #3
mr.loops
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Limp mode can be caused by numerous reasons

What codes did VCDS show ?


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Old October 8th, 2019, 08:42   #4
UncleSpence
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Quote:
Originally Posted by mr.loops View Post
What codes did VCDS show ?
It's showing P0234 Overboost

I can also confirm that the title is misleading. As mentioned yesterday, immediately after parking it, it fired right up. Now it's sat 24 hours and doesn't start at all.
I'm pretty confident however, that if I gave it a little nudge with some gasoline fumes in the intake that it would start and then run just fine. If this car had a lift pump I'd start there, but I am not personally aware of one on the alh.
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Old October 8th, 2019, 09:04   #5
Jetta_Pilot
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You might find some answers here, 3 video clips and more. Good luck.



https://www.google.com/search?client...-d&q=p0234+tdi
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Old October 10th, 2019, 04:19   #6
putnummayhem
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https://www.kermatdi.com/c-107-kits-...pair-kits.html

May help
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Old October 10th, 2019, 04:22   #7
putnummayhem
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Or

http://www.myturbodiesel.com/1000q/m...de-TDI-fix.htm
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Old October 10th, 2019, 09:34   #8
BobnOH
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http://wiki.ross-tech.com/wiki/index...8/P0234/000564
Look over the big air piping.
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Old November 7th, 2019, 15:23   #9
UncleSpence
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Did a bunch more digging and this is what I learned along the way. Always hate a thread that was never resolved.

No start issue was injection pump losing its prime. After some inspection, I saw that it had a leaky seal somewhere. Would run great so long as it was never turned off. I drove to TDIGuy in Fort Worth, Texas and his crew did the injection seal for me and helped me do some troubleshooting for the limp mode.
After some vacuum testing narrowed it down to the turbo actuator has a leak somewhere so it's not regulating the boost properly and causing it to overboost and go into limp mode. I'll fix that when I feel inclined or have a big trip planned.

A few weeks after the injection pump seals replacement, we had a cold front and I started the car for my wife, came back out and it wasn't running anymore. It had been slow starting a few days before that, and required some additional cranking before firing up. Was really frustrated with it and started back to troubleshooting and forum searching. Could be a lot of random things with these gremlin filled cars. They're reliable as crap on the highway but have lots of little demons crawling in them chewing on wires and vacuum lines. I replaced all the fuel hoses from the fuel lines to filter, hoses filter to injection pump, new filter, and new tee that is on the return line in the filter itself. Primed the pump and with a little persistence it started again and has run and fired up well ever since. Was technically a two fold problem with the injection pump losing its prime, but should be resolved for a while.
Special shout out to TDIguy in Forth Worth for the injection pump reseal and putting me in queue and getting me on my way within one day and another special shout out to Thomas from the Youtube channel Thomas EXOVCDS for his help as well.
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Old November 7th, 2019, 16:18   #10
BobnOH
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Thanks for the follow up!
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