The engine in question is from an 2002 Audi A4 1.9TDI PD, engine code AWX. The problem with this engine started a few months ago, when it started to shake under heavy acceleration in 1000-2000 rpm range. If you would accelerate half the pedal, it would accelerate without any shaking. The problem was ignored until it wouldn't start at all if the engine was sitting for a couple of hours. In the morning it would start only with a starting spray or if towed. I then decided it's the tandem pump, so I switched with another one. The problem was solved, but in an attempt to repair the old one, I then switched it back and put on the fuel return line a one way valve that was holding the pressure inside the tandem pump to about 0.5 bar. My conclusion was the the tandem pump was leaking fuel, therefore it would not start. The engine was running like this until a few weeks now, when it started shaking at idle so hard, I am worried it could tear the timing belt apart! At about 1200 rpm, the shaking is somewhat dissipated but it's now shuddering even at part throttle until 2000 rpm. If you keep the engine over 2000 rpm, you can easily reach 100 mph! Tomorrow am I posting a video for you guys to see the engine shuddering. Ok, now here's the list of what was done on the car: -timing belt was changed about 1 year ago. -DMF was changed 2-3 months ago, before all these problems appeared; -all filters and oil was changed due to interval; And this is what was done since this problem occured: -check the fuel tank for debris/water -fuel filter change -timing check -tandem pump switched -compression test: exactly 30 bar on all cylinders! -NO VAG COM ERRORS! I have checked the idle speed smooth running control via vag com and this is what it was showing right after start up http://i.imgur.com/XT0BwHQ.jpg And this was showing after at least 1 minute of idling http://i.imgur.com/4H2JPRx.jpg Could it be the injectors? If yes, which is the main suspect? I'm literally running out of ideas. Thanks for patience reading this. I really need your help guys!