Hey Ross yes the throttle body is self adjusting but when you clean it out yourself, it requires setting back to the basic setting via. the diagnostic machine, VAG5051> 01. Engine Electronics> Adaption>Channel 30 0r 60> Adaption runs> Adaption OK, its not as simple as just turn ignition on wait 30 secs.
To test the dump valve you would require a midi-vac ideally, remove the dump valve and use the midi vac to open and close the valve manually to see if its sticking or not, or you could attach a piece of pipe to the dump valve and suck n blow it to operate the valve to see if it sticks. Usually when your coolant temp sensor goes it brings on an engine light unless the fault is recorded as sporadic(intermittant) then it will just stay in the fault memory and the light will come on now an again.Worth a try they only cost a couple of quid and pretty easy to change yourself. Again Air Mass meter is pretty common on the VAG vehicles but you can usually tell, if its a suspected air mass meter disconnect the sensor and have a drive with the sensor disconnected, this is located on the pipe on your airbox, with it being disconnected the ECU tells the car to go to basic settings and makes an estimate of what air should be going in which is usually pretty accurate, if the car runs better then its ur air mass meter, if same then you can rule that out. Also maybe theres an air leak somewhere, buy yourself some brake/clutch cleaner or carburettor cleaner, start the engine and then spray some of this onto all the vacuum pipes and pipes leading to turbo, if the engine revs itself, it means theres an air leak somewhere, which can cause the symptoms that you describe, main place where i have found the air leak is the pipe from your airbox to the turbo, but you have to reach right down to the turbo to feel it as it splits where it joins the turbo, this is a pretty common fault and have witnessed this a few times, best thing is too do it from underneath the vehicle as you can visually see it better. Next thing would probably be the N75 as this controls the boost, cnt really check these without a diagnostic machine,but these are also common but wudnt do this till you have checked and done all the cheaper things lol. Play in the turbos impellor bearing could be another reason, does the vehicle excessively smoke, etc. can feel this manually by taking off hose and sticking fingers in and having a wiggle, if none of these things cure it, the
problem may be something a little deeper i.e leaking valves, lambda sensors, coil packs, Injectors, sumtimes even an ECU or bad connection to the ECU, could try cleaning all the earth points in the engine thats worked for me a few times.
Let me no how you get on
alex (ishmo)