2000 Audi A4 Just bought a used Audi A4 and has a few probl

I just bought the car so I don't know the correct category and if the problems are related or not. But the 1st problem is that a check engine light is on but it will not connect to the code reader at a couple places and the fuse is okay. Second is the engine stutters when accelerating especially under hard acceleration at around 40 and 80 mph typically around 5500 RPM. Third the transmission after being driven around a bit will get rough shifting from P to D and when I put it in Reverse and hit the gas pedal the car shakes violently.