My E46 320D MSport Help/Advice please??

Can anyone give me any advice on a recent problem. My engine warning light comes on after about 3500 revs when the MAF sensor is disconnected and the car seems to slow up a bit but if I connect the MAF the car is crazy slow altogether. I've originally cleaned the MAF but that didn't work so I got a new one which also made no difference. I then cleaned the EGR valve and the intake manifold and there was a tiny improvement but I still suspect the MAF sensor. I have also replaced the Glow Plugs. The car also idles rough on start up until it warms up and is fine again. I've had the car plugged in by a friend and the codes P0102, P0112 and P3002 came up. The first 2 codes are circuit low codes and the last one is a manufacturer code. I'm wondering if this might be a wiring problem but I don't want to spend any more money on things that might not make a difference so I'm hoping somebody here might be able to help me from past experience or superior bmw knowledge??????