power cutting out.

[okron1k]

my dad has a mk3 tdi and the power will cut out around 120 km/h. the weird thing is, if i turn the car off and back on again i can continue going faster with the power restored.

i noticed that if you accelerate very slowly to 120 km/h you can slowly go faster without the power cutting out but it's as if the car reaches a certain amount of boost and gives out. again, turning off and on the car (without stopping) fixes it.

any idea what this could be? my own idi's never had that feeling of power loss.. and the fact that turning the car off and on will "reset" it means this must be something electrical..

[Vincent Waldon]

Your dad is experiencing a very classic TDI behavior known as "limp mode"... the ECU detects (or thinks it detects) that the turbo is overboosting and shuts it down to avoid further damage.  Power-cycling the ECU makes it forget and start over.  Your IDIs have never done this 'cause they don't have an ECU.   

There are many many many possible causes.. your best bet is to do some searching over at TDIclub.com.... there's a million years of discussion on this and at least one good stickie thread iirc.

Step 1:  get the car scanned with VCDS for codes... the car is likely trying to tell you what's wrong.

[catlin_cava]

my bet its Limp mode and it might be somehting caused by the turbo(vaccum leak), my MK4 TDI would get gutless and throw limp modes, I had a few bad vacuum leaks and a bad N75 valve.

Check your Vaccum lines

[okron1k]

interesting. i figured it was something like this to protect itself, but there is no CEL? also just recently took out another tdi for a drive from the same guy that we bought my dad's from and i managed to get limp mode on it too. guess my foot is too heavy for an ecu

[Vincent Waldon]

but there is no CEL?

In the first gen TDI there's stuff that happens without a code being set, there's stuff that happens that sets a code but was not deemed worthy of throwing a CEL, and then there's stuff that happens that throws a code and a CEL... or a CEL and/or a flashing glow plug light.  The latter was reserved for stuff like a burnt out brakelight bulb.   

Ergo... step 1... scan it for codes (even if it isn't throwing a CEL). 

There are also two kinds of codes:  general OBD2 as required by law, and VAG-specific.  Generic OBD2 scanners like the kind Autozone or Partsource will let you borrow only cover off on the first... VCDS is required to really dig into the VAG-specific stuff.

[catlin_cava]

interesting. i figured it was something like this to protect itself, but there is no CEL? also just recently took out another tdi for a drive from the same guy that we bought my dad's from and i managed to get limp mode on it too. guess my foot is too heavy for an ecu

my car only thru a CEL when it went into LIMP and I got mad and threw it down a gear and held her to the floor then she shut right off on me lol.

Just because there is no CEL doesn't mean there isn't a code.

[nathan_b]

I wager that the wastegate is stuck shut.

[Vincent Waldon]

I wager that the wastegate is stuck shut.

Yup... on both cars.   

[okron1k]

super late reply, sorry.. was looking through my old posts and forgot about this.

i don't have a vcds (is that the same as a vagcom?) or an obd2 scanner (all my cars have been non-TDI's)

is the wastegate getting stuck a common issue? is it a simple fix?