Hey everyone, I need help guys this is my last resort. I have been having trouble with this car for the past 2 months. I have not been able to drive it except to see if it is fixed. So any help would be greatly appreciated. So about 2 months or so ago I was driving the car and there were no real problems except for the slight miss it had as it needed new coils. Then I got annoyed with not being able to here the car as I live in the country and every car is excessively loud and I shift off of the sound of the engine usually. So I cut off the muffler with the exhaust tips on them and the one before that that is smaller. I drove it for two weeks or so and then I got the new o2 sensors and I had them put in by a friend who is a mechanic. And he put the new one in and then realized that the other o2 sensor was a post cat not a pre cat as I ordered 2 pre cats. (Replacing o2 sensors because the obd2 saved it needed bank 1 sensor 2 and the other). So my friend took the o2 sensors out and put in the old ones and that was it. He cleared the codes and called me. I get over there the next day and I test drive it. Immediately I realize something is not right. The car would loose power around 2500+ rpm, and after a minute or so of driving the car would start missing and it would sound like it was running on 3 cylinders or less. So I take the car back and tell him and we try to figure it out. And as we are both not bmw specialists we are stumped. So we limp it back to my house (right down the road) and park it. After awhile of searching I came up with nothing. So I put it on a trailer and drive it 1 hour away to a euro mechanic. He says he can't figure out what is wrong with it as he can't drive it to reset the computer to check the computer. But he does say it needs a new ccv valve and it need the exhaust back on. So I trailer it back home and then I put back on the resonator and test drive it again. After the resonator was put back on it seemed to not loose power as soon and it seemed to run a little longer before missing but this could just be being optimistic. Now the car is sitting in my front yard (and doesn't make to bad of a yard orniment) waiting to be fixed. Also the car was bought needing a whole cooling system which was replaced and it needs a sensor or something for the fan as it overheats in traffic cause fan does not turn on. Has a k&n drop in and new spark plugs. Also upon thinking more the car might not have had the exhaust for more like a month. And please this is my only car and also the first car I bought myself, I love it but I am grtting tired of driving my grandmother's Buick century to work. I am willing to fix it but it is also up on Craigslist for sale. NEED HELP BAD!!!!!!!