2.0 Tdi GT sluggishness, hesitant and limp mode please help!

[Hobbit619]

Hi guys, first time poster so please go easy! I really need some advice because I'm at a loose end.

I have a mk5 golf 2.0 tdi, and it keeps going into limp mode when I accelerate over 70mph. This is extremely annoying considering I drive to Bristol from plymouth to see the girlfriend! 

Driving around town sometimes it is hesitant to accelerate, and it judders when I am driving really slowly but it is otherwise normal. The emissions engine light is permanently on as well. The engine will also idol a little high (1k revs as opposed to usually just under) and slowly fluctuate. The fault codes that have come up are boost pressure sensor too low signal, engine coolant temperature circuit high input, and turbo/supercharger under boost.

Taking it to the garage, they have changed a temperature sensor (?) to no avail, and have said that if that didn't work, they thought it would be a new vacuum solenoid at £250. Following from the fact that changing the temperature sensor didnt work (shock), I replaced the vacuum solenoid myself for £25. This did not work either, so I'm so glad I didn't take the garages option!

I have been told that it isn't the turbo, and it is not making any strange noises that would otherwise be telltale of a fault, so fingers crossed.

So this is where I am now, begging for some help. I am praying that it's not something expensive, I am a student and need all the pennies I can get.

Thanks in advance!

[jason_rmh]

I've recently had this on my TDI.

Googling limp mode normally brings up threads indicating faulty turbo or sticking vaines (inside the turbo).

There could be a number of other causes:
Vacuum leak
Boost hose leak

Unfortunately it will take some diagnosis / testing to get to the cause or to rule things out, which maybe your garage doesn't want to do.

Firstly, a scan with vcds to see why limp mode is happening.
It's either underboost or over boost condition that is triggering limp mode to protect the engine.

Mine was an over boost condition.

Same as you, I replaced the vacuum solenoid.

I vacuum tested all hoses coming out of the vacuum solenoid to ensure no leaks.

You can then pressure test the boost hoses which will show any major boost leaks.

You can try to free up the turbo without removing it from the car using the 'mr muscle' technique which involves squirting oven cleaner into the exhaust side of the turbo (remove downpipe).

I eventually found my problem was sticking vaines on the turbo meaning the turbo was over boosting but also, the boost hoses that connect to the turbo, with a 90 degree bend, had split and was not visible until the hose was removed from the car.

Hope this helps.

It is very frustrating. I put up with it for a while, but it eventually started popping boost hoses off due to the overboost.

Jas

[Leco_GTI]

I had a similar problem but mine is a GTI. Massive loss of power, juddering and eventually going into limp mode but only when sitting on traffic, never while I was driving. The problem was a split cable that connects to the boost pressure sensor. All symotoms and codes indicated a turbo failure but gladly it was not. Seems to be common in the GTI's.

[jason_rmh]

I had a similar problem but mine is a GTI. Massive loss of power, juddering and eventually going into limp mode but only when sitting on traffic, never while I was driving. The problem was a split cable that connects to the boost pressure sensor. All symotoms and codes indicated a turbo failure but gladly it was not. Seems to be common in the GTI's.

This is a good point.
On the TDI, the MAP sensor is located on the plastic pipe connected to the passenger side of intercooler.

Check the wiring and probably worth giving the sensor a clean with carb cleaner.

You could also do a resistance check to see if the sensor is faulty.
Another way to tell, is to check the sensor in vcds.
If the sensor is faulty, the car will default to atmospheric​ pressure value rather than the value from map sensor.

Jas

[Hobbit619]

I had a similar problem but mine is a GTI. Massive loss of power, juddering and eventually going into limp mode but only when sitting on traffic, never while I was driving. The problem was a split cable that connects to the boost pressure sensor. All symotoms and codes indicated a turbo failure but gladly it was not. Seems to be common in the GTI's.

This is a good point.
On the TDI, the MAP sensor is located on the plastic pipe connected to the passenger side of intercooler.

Check the wiring and probably worth giving the sensor a clean with carb cleaner.

You could also do a resistance check to see if the sensor is faulty.
Another way to tell, is to check the sensor in vcds.
If the sensor is faulty, the car will default to atmospheric​ pressure value rather than the value from map sensor.

Jas

Thanks for the advice guys, I really appreciate it, I have done a bit of research on the Mr Muscle stuff but there doesnt seem to be any information as to where it needs to go, how I get to the outlet etc, any help would be greatly appreciated

[andy1979uk]

I had the same issue on my passat tdi, tried to clean it using a kit from the internet. It helped a little but doesn't really get to the areas that are blocked. In the end just bought a recon turbo 240 delivered and it drives like a new car.

[Leco_GTI]

I had a similar problem but mine is a GTI. Massive loss of power, juddering and eventually going into limp mode but only when sitting on traffic, never while I was driving. The problem was a split cable that connects to the boost pressure sensor. All symotoms and codes indicated a turbo failure but gladly it was not. Seems to be common in the GTI's.

This is a good point.
On the TDI, the MAP sensor is located on the plastic pipe connected to the passenger side of intercooler.

Check the wiring and probably worth giving the sensor a clean with carb cleaner.

You could also do a resistance check to see if the sensor is faulty.
Another way to tell, is to check the sensor in vcds.
If the sensor is faulty, the car will default to atmospheric​ pressure value rather than the value from map sensor.

Jas

Hi jason_rmh, mine was not the MAF sensor. This one on the GTI is easy to locate as it sits on the air intake hose on top of the engine cover. I believe the boost pressure sensor is near the turbo and needs a lot of dismantling to get there. I was charged 4 hours labour but that includes the diagnostics, testing, etc.

[jason_rmh]

Yes, MAP not MAF.

[Leco_GTI]

I just read about it. Always learning something