Problem 1 - Car starts to shake at random times becoming more and more common. Engine light does not flash, I usually pop it into neutral and park it and wait 2-10 min for car to stop shaking. Mabey it's a coil pack?

Problem 2 - Car was idling around 1100 rpms and was shaking while idling. Now car is no longer shaking while idiling and runs at 900 rpms now.

Problem 3 - Car feels like it is underpower at sometimes, engine sounds normal and turbo sounds normal.

Car Info.

2004 Audi A4, quattro, sports package 1.8T. 140,000 km. Just had third cylinder mis-firing, got coil pack changed. Ran fine for 500km engine started to shake random times along with cel flashing.

 

Update - When the car shakes the exaust sounds like it has something stuck in it, almost coughing. Also took a look under the hood while it was shaking and the engine was shaking from side to side.

 

Dida bit of research on faulty valve purge
into it and it does sounds it failed while open. Depending on how it failed, it usually is one of two different symptoms. Both will turn on the check engine light, and store a code. If the valve fails in the stuck open position, the engine will run rough and not idle correctly.