Im having some trouble with my A6 1.9TDI PD, AWX, 130HP engine, year 2002. It has been running very fine over the last 5 years, but know Im having an issue with the boost control. Upon accelerating, the boost suddenly spikes, and gives a little kick in the back. Certainly not very healthy with a cold engine and -5 degrees outside. The engine does not react smoothly to pedal movements, and Im also sometimes having a trouble code when reading out with VAGCOM: 17964 - Charge Pressure Control: Negative Deviation P1556 - 35-00 - - After having a long run on cruise control, the car refuses to accelerate when pushing the pedal, or only a tiny bit, then it gives the trouble code. Looks that it does not want to accelerate due to the absence of boost. (charge pressure control valve stuck in no boost position?) Ive already checked the N75 charge pressure control solenoid valve, I measure 19 ohms (correct value according to workshop manual). I can move the turbocharger actuating rod, moves smoothly, but it needs quite some force to move, dont know if this is normal. Anyone has an idea what else I should be looking for?