Have you tested the throttle body / changed map sensor on the pipe underneath from intercooler on left side / unblocked the link pipe from the egr at the front to the egr cooler and boost pressure actuator at the rear, and checked you have no boost leaks from the turbo to and including the intercooler? If so Could be the Variable Geometry Turbo has had it.
So far I have changed the map sensor, eliminated leaks from the turbo to the intercooler and from the intercooler to the inlet manifold. Removed the egr valve and cleaned it, removed and cleaned the throttle body, cleaned the link pipe to the egr cooler, had the engine carbon cleaned, vacuum tested the egr actuator, and vacuum tested the boost pressure actuator, vacuum tested all vacuum lines from the control unit to the actuators, as well as the vacuum reservoir and vacuum supply and returns. All that is left is change vacuum control unit, clean the egr cooler assembly that bolts onto the turbo, clean the turbo in case the vanes are stuck together (has to be done cold or the Mr Muscle gums up), remove and clean the inlet manifold, clean or replace the intercooler, change the Engine control module (ECM) and or replace the turbo. I will post as I do each bit, hopefully one of these steps will fix it.
So I replaced the vacuum unit and alas no joy but now have the P0236 code and a strange noise coming from the vacuum unit when the ignition is switched back on after engine running and all codes reset. I think it will come down to the vacuum actuator bolted onto the bottom of the turbo even though it holds a vacuum I am starting to suspect that the diaphragm is old and too stiff to allow the VCU to operate it and calculate the correct atmospheric pressure. I did the Mr muscle thing which seems to have made the car run a lot better and I can move the actuator rod somewhat freely but seems very stiff from the actuator side again leading me to suspect this actuator is at fault. So I think the next thing to do is to get the actuator off and replace it. Might have to remove turbo in order to do so, so if that's the case I will strip the turbo down and clean it thoroughly. I will post a further update when done.
So I replaced the vacuum unit and alas no joy but now have the P0236 code and a strange noise coming from the vacuum unit when the ignition is switched back on after engine running and all codes reset. I think it will come down to the vacuum actuator bolted onto the bottom of the turbo even though it holds a vacuum I am starting to suspect that the diaphragm is old and too stiff to allow the VCU to operate it and calculate the correct atmospheric pressure. I did the Mr muscle thing which seems to have made the car run a lot better and I can move the actuator rod somewhat freely but seems very stiff from the actuator side again leading me to suspect this actuator is at fault. So I think the next thing to do is to get the actuator off and replace it. Might have to remove turbo in order to do so, so if that's the case I will strip the turbo down and clean it thoroughly. I will post a further update when done.
Hooray managed to sort it, so having done all the above I still got the P0236 code for over boost re boost sensor so I decided to pull out the MAP sensor on the lower boost hose on the lower front left (underneath) of the car and clean it. Having removed it and cleaned it with brake cleaner I replaced it only to find that the code came back immediately I turned the ignition on. That proved to me that sensor was now caput and possibly the issue, so I swapped it out with the old VAG MAP sensor I had previously removed thinking it was bad, and hey presto no P0236 code. I think what finally cured it was a combination of cleaning the turbo with Mr Muscle, making sure there were no leaks, and replacing the vacuum control unit (VCU) which I think most likely solved the P0401 EGR system performance code. By the way the VCU now makes all the right noises as it pressurises the system which the old one didn't do. I also reassembled every connection with a thin smear of Vaseline to re-engorge the rubber so that the seals were as good as they could be, including on the VCU male connectors on the multi connector block of the VCU. Only thing left now is to have a look at the glow plug wiring harness as I have issues there as well. I will probably leave installing the new wastegate actuator and dismantling the turbo until I get time to do a full service on it as its running really well now and goes like lighting - its really fast!!! Hope this helps and as a side note in future I would only use a genuine VAG MAP sensor as the 'replacement' was aftermarket and clearly not up to the job. All the best Crowie.
Hooray managed to sort it, so having done all the above I still got the P0236 code for over boost re boost sensor so I decided to pull out the MAP sensor on the lower boost hose on the lower front left (underneath) of the car and clean it. Having removed it and cleaned it with brake cleaner I replaced it only to find that the code came back immediately I turned the ignition on. That proved to me that sensor was now caput and possibly the issue, so I swapped it out with the old VAG MAP sensor I had previously removed thinking it was bad, and hey presto no P0236 code. I think what finally cured it was a combination of cleaning the turbo with Mr Muscle, making sure there were no leaks, and replacing the vacuum control unit (VCU) which I think most likely solved the P0401 EGR system performance code. By the way the VCU now makes all the right noises as it pressurises the system which the old one didn't do. I also reassembled every connection with a thin smear of Vaseline to re-engorge the rubber so that the seals were as good as they could be, including on the VCU male connectors on the multi connector block of the VCU. Only thing left now is to have a look at the glow plug wiring harness as I have issues there as well. I will probably leave installing the new wastegate actuator and dismantling the turbo until I get time to do a full service on it as its running really well now and goes like lighting - its really fast!!! Hope this helps and as a side note in future I would only use a genuine VAG MAP sensor as the 'replacement' was aftermarket and clearly not up to the job. All the best Crowie.
