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Hi,
It sounds like the turbo boost isn't being controlled properly, but this could be due to several things. Check for splits in the air pipework, and then get the N75 valve checked out - this is the item that opens the wastegate on the turbo, effectively shutting the turbo off. Oh, and check that the wastegate actuating lever isn't seized up...
Hope this helps you a bit. D.
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Its not your clutch. Its one of three things which is regards to your turbo. 17958/P1550/005456 - Boost Pressure Controle Valve (N75): Control Deviation
Possible Symptoms
Irregular behaviour
Reduced power output
Limp mode
Possible Causes
Hoses/Pipes incorrect connected, disconnected, blocked or leaking
Charger Pressure Control defective
Solenoid Valve for Boost Pressure Control (N75) defective
Turbocharger defective
Possible Solutions
Check Hoses/Pipes to/between Components
Check Charge Pressure Control
Check Solenoid Valve for Boost Pressure Control (N75)
For VW TDI: Fault code P1550 = "Charge Pressure Deviation" You must check up all vacuum hoses, the pressure charge air line (pressure hoses, spring-type clips, charge air cooler), the vacuum reservoir and also all solenoid control valves.
You must try follows if you are able to do this: 1. Engine stopped and ignition switch off. Check all pneumatic connections and hoses between turbocharger actuator = pressure unit for boost-pressure control, boost-pressure control solenoid valve, vacuum reservoir, EGR control solenoid valve, intake-manifold flap solenoid valve, EGR valve with throttle - part of intake manifold. Also the vacuum connection between tandem pump and brake booster. If you find something wrong replace parts. If not go to step 2. 2. Extract the hose of the turbocharger actuator = pressure unit for boost-pressure control part of turbocharger. Instead of the original hose you must place another 1 meter long hose with the same inside diameter, and then you check to inspire yourself the air from the other one extremity of this hose. The mechanical connecting rod of the turbocharger actuator must have a smooth and whole motion. If you can do that with your mouth, then you must replace the boost-pressure control solenoid valve. If you can not reach this with your mouth, then you go to step 3. 3. This is the most difficult work. The problem is that the soot particles deposits inside the turbocharger plugging the variable nozzle geometry mechanism = adjustable vanes of the turbine. If the turbocharger actuator is not able to adjust the turbine vanes the charge air pressure increase too much and ECU (engine control unit) go in "limp mode" = engine protection software. As a result the "limp mode" engine still running until you turn the engine off (ignition switch off) and back on when the "limp mode" is deactivated. 4. You must be able to extract the turbo from the engine and then to disassemble the turbocharger, clean inside adjustable vanes mechanism and refit all. It is some work to do here, but after that you will be full satisfied!
Sounds like the car is going into limp mode, and then resuming normal operation the next time you start it. This is probably due to an overboost or under boost situation. If this is the case, the car's computer can't effectively control the boost the turbo is producing, so it just "turns" the boost off. Ask the shop what the engine code was specifically, and then compare it to VW specific codes. ( google "VW OBD codes"). I'm betting the code is either P1556 (boost control negative deviation, underboost), or P1557 (boost control positive deviation, overboost). Proper diagnosis with VW specific software is half the battle. The rest is methodical troubleshooting by you or your shop so you don't replace parts that don't fix the problem. No offense intended, but it sounds like you need to bring your car to a shop that knows VW's. Sorry I'm not more helpful, but without more info, I'm just taking a guess. I've actually had this problem with my Tdi, and the fix was cleaning the intake manifold and a slight turbo actuator adjustment. But, in your case, several things could cause this which is why proper troubleshooting is important. Hope this helps.
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