2002 BMW 330ci Juddering at low revs

I have a bmw 330 ci and I brought it off a turkish man so I didnt understand properly what he said he had done to the car but it had a paddle shift gearbox but he took it off and put a manual one on there ( didnt even put 3 bolts in the bottom of the gearbox). He said he had his mate remap it but didnt get no recite as his mate done it free. The engine is tapping but im not sure if its the engine or vanos but my main concern is the lack of power it has has under presure, under 3000 revs it judders really bad and dont have much power but over 3000 rpm it seems fine and thats engine hot or cold.I put it on diagnostic and it come up with o2 sensors and air problems including maf so I brought another one and cleared the codes, I then started the car for accouple minutes turnt it off then done the diagnostic again and the codes where gone but it still has the problems.I pulled the wires off the maf and the throttle body while the car was on tic over and the car was still ticking over the same where as I thought the engine would stall. Theres also 3 wires that clip in near the injectors and 2 of them have been cut off but 1 is still clipped in. This is a petral non turbo 330