Recently on three longish journeys from Suffolk to Liverpool and to and from South Wales engine power has suddenly dropped as if the turbo has cut out. It would maintain the speed I was doing but refused to go any faster.No warning lights came on and there was no increased noise from the engine. Once the engine was switched off for a few seconds and restarted it ran normally. On asking the local dealer it was at first said that it could be a senser and there was nothing to worry about. On a second visit it was plugged into their diagnostics and they said that no fault was found. However they said that the turbo could be on the way out. The turbo isn't making any untoward noises or whistling. Any ideas on the problem would be appreciated. The car is a a non CR 2.0 TDI with 37000 miles on the clock, has been regularly dealer serviced and the cam belt etc changed last October.

Thanks in advance for any replies even if they are all doom nd gloom.

You really need to get it scanned.

If you find an overboost fault code, then it's possibly down to sticky canes on the VNT inside of the turbo.

This adjusts the angle of the vanes to provide the correct boost, in place of a waste gate, however if it sticks, then too much/little boost can occur.

If this happens, the car effectively "turns off" the turbo to reduce the chance of damage.

These can be cleaned by a good garage, otherwise there are good companies out there who will sell recon units (look on here for reviews).

Hope that helps.

Yes the dealer will tell you the turbo is on the way out. He makes a load of money by doing so. There will also be a lot of people here talking about soot and coked up turbos.

It is never that simple. I struggled with diagnosing Limp Home mode for months. There was a MIL/CEL light only once (Overboost condition). I did see a fault code that related to the imobiliser. This is because I switched the engine off and on to clear the limp mode. The imobiliser needs 10 seconds to cycle and throws a code if you are switching off and on quickly.

Anyway, the test for the turbo is a simple vacuum pump with guage (cost around 50 quid). I bought this one http://www.amazon.co...ils_o00_s00_i00

Your mechanic needs to supply vacuum to the turbo actuator and see that the VNT vane leaver is moved by the actuator rod moves when commanded and stays retracted at the full vacuum. The guage will also check the vacuum at the solenoid when the engine is switched on. This is the VAG approved test.

From the service manual:

For the inspection use a mirror.

• Specified value: 50 ...120 mbar (0.005…0.012 MPa): the tension

rod must move up.

• Specified value: 550...620 mbar (0.055…0.062 MPa): the tension

rod must be positioned at the top up to the stop.

If your mecahnic is diagnosing a busted turbo without doing this simple ten minute test (no labour involved) I would suggest a new mechanic.

In my case I was seeing a gradual decrease in fuel economy and I replaced the Mass Air flow MAF sensor. This didn't cure the problem because the MAF doesn't cause it. However it did improve the car's performance and economy markedly.

A few miles later I replaced the MAP Manifold Air Pressure sensor. - Instant sucess. The car runs like it did when I got it. It's hard to say with intermitant fualts that cause Limp mode but I think I have it in remission at least.

Without a fault code. I also suspected underboost and I replaced a leaking intercooler seal for €7.

I paid €170 for the two sensors. IF, as an example, you replace the MAP sensor you might cure your problem for under fifty quid.

My advice is: eliminate all the possible causes and replace parts only when they are shown to be faulty and or cheap.

Pay for a new turbo only when you are sure it has been diagnosed. Refuse to let a mechanic throw parts at the problem. As I said the test can be done DIY and the tools are mechanical rather than a plug in computer and Cheap!

HTH