My uncle called to me this evening with his B6 1.9 TDi (AVF) 130bhp quattro which isn't running right. It's covered 210,000 miles. At tick over and right through the rev range it sounds like it's running on 3 cylinders, there appears to be a "thumping" coming from the engine. When I had the pipe to the airbox off, the thumping was resonating loudly through it and when I had the intercooler pipe disconnected it was even louder, really booming (not unlike a blown exhaust). On driving the car it's down on power, but isn't so bad that you couldn't pass something, it's at about 70% of what it should be. I was thinking a faulty injector at this stage and presumed my VagCom would pick it up. I ran the VCDS on it but no codes came up. I went into the measuring blocks (Engine / 13) to see how the injectors were performing and while the "Idle speed smooth running control" remained within tolerance, -2.8 to 2.8 mg/H they seemed to be all over the place. Approximate reading were Cyl1: -1.0, Cyl2: -1.5, Cyl3: 1.0, Cyl4: 1.1, on revving the car they didn't alter too much and never went outside tolerance. I'm thinking camshaft wear or/and wear to the lifters at this stage, but before I go ripping has someone else come across this before. I don't think it's an injector failure as the VCDS should pick up on that. This problem appears to have started overnight. Any help would be appreciated, thanks.