mk4 tdi check engine light

[thegooddie]

hey guys, this is going to be kind of tough to explain but i'm going to do my best.
i got a mk4 tdi and its chipped (by the previous owner) now i've found that when going full throttle in 5th gear the car goes into what i'd call "limp mode" at around 150. pretty much the power cuts out and it feels like my turbo shuts off. the solution to this is just to turn the car off and start it again and the problem is gone.

i had been told that the problem is my throttle control censor..something to that effect.

today i was on my way to edmonton and on the highway i went into limp mode so i pulled over, waited a few seconds for the engine to cool down, turned the car off and started it again and everything was fine, but now my check engine lights is on..

any ideas as to what that may be? how bad could it potentially be to drive home like this? i'm not sure if i'll be able to get it checked out in edmonton or not.

any input would be appreciated..

thanks and happy holidays

[BaggedGLI]

Re: mk4 tdi check engine light

As long as its not flashing it will be fine to drive home. Get it scanned and it should tell you right away.

[onceover]

Re: mk4 tdi check engine light

Sounds like the exact same issues graemes been dealing with

http://www.eurodrivers.ca/forums/showthread.php?t=20742

[Stonewall]

Re: mk4 tdi check engine light

Just don't go 150? Follow Graemes thread for possible fixes. When the same thing was happening to me though the turbo was on its way out, it tried to escape via the intercooler and failed...

[shconer]

Re: mk4 tdi check engine light

Sounds like it might be setting a over boost code. Mine has done that once before.

[thegooddie]

Re: mk4 tdi check engine light

what did you do to fix the problem?

Sounds like it might be setting a over boost code. Mine has done that once before.

[Benjamin]

Re: mk4 tdi check engine light

Fix to the problem that was described can be a few things. I had the same thing and would push the clutch in and turn the car off for a quick sec, turn it to on and let the momentum start the car.
Over boost, could be a seized VNT actuator, or a N75 Valve. Mine was the N75, cost is not crazy and easy to replace yourself.

MK4, which year exactly is it?

[stefan]

Re: mk4 tdi check engine light

When my mk4 did this, it was the turbo, but that was at the dealership. I'm thinking the dealer probably replaces the whole unit even if it is just the VNT actuator. All I really know is they replaced the turbo, but I don't know why.

[thegooddie]

Re: mk4 tdi check engine light

mk4, which year exactly is it?

2000

[shconer]

Re: mk4 tdi check engine light

Mine only did it once and it was a hot day and I was going 150+, It was probably due to the Diesel tunning box. If you have got a real tune I would agree that it is probably something wrong with the boost control or the turbo.

[dJ]

Re: mk4 tdi check engine light

Kind of sounds like it is starving for fuel. Maybe not though.

[Red90]

Re: mk4 tdi check engine light

You need to find out the exact codes, then report back.

If it is the throttle sensor, then it is easy to fix. The throttle is just a very simple potentiometer connected to the throttle pedal. Take the assembly out of the car (5 minutes), remove the cover over the switch brushes. Clean the contact strips and brushes, which normally fixes the problem. It is a very simple job.

[thegooddie]

Re: mk4 tdi check engine light

You need to find out the exact codes, then report back.

If it is the throttle sensor, then it is easy to fix. The throttle is just a very simple potentiometer connected to the throttle pedal. Take the assembly out of the car (5 minutes), remove the cover over the switch brushes. Clean the contact strips and brushes, which normally fixes the problem. It is a very simple job.

yeah i need to get on that. gonna take my car to George to get him to take a look too. just so busy these days. the car's parked though until i get it checked out

[jiggseob]

Re: mk4 tdi check engine light

I'd bet my last buck you are getting an overboost code:

16618/P0234/000564
=== 16618/P0234/000564 - Boost Pressure Regulation: Limit Exceeded (Overboost Condition) ===

The N75 valve is an open-shut thing. Power-on = open, power-off = closed. Variable nozzle turbo actuation is a graduated adjustment that goes from full-on to full-off and every adjustment in between.

How does a computer, and on-off mechanism, accomplish an infinitely adjustable range? It opens and shuts the valve quickly, and more quickly it opens and shuts it, and the longer the open pulses are, the more the turbo nozzle is actuated. Its the duty cycle, if the power is on 10% of the time the valve is open 10% of the time, and the boost is less. If the valve is open 90% of the time, the boost is more. So opening and shutting the N75 valve rapidly gives a variable amount of vacuum to the VNT actuator. There's a port in the N75 valve that allows vacuum to leak back in with the power off to equalize (leak-down) the vacuum. IF the actuator is rusty and stiff, if there's a leak in the old hard and cracked vacuum line, if theres extra carbon on the turbo vanes, if the VNT pivot shaft is a little corroded on its pivot, the system may not work right. There's your code.

The dealer solution is to replace parts until it works right, starting with the N75 valve, and going up to the turbo. It could be as simple as an old cracked vacuum line. Start there.

While you're under there replacing the line to the vacuum pot on the actuator, use a mity-vac to suck on the actuator, and see if it moves. If you can't move the actuator with the mityvac, the actuator is pooched. That was the problem in both of my ALH tdis, a 98 Beetle and my 03 Jetta.

There's a vendor (from Calgary I think) on this forum that will probably get you a VNT actuator for $150 or so.

The dealer solution for a pooched actuator will be $2k+ for a new turbo.