Well, its a BMW 323i and what happens is that when its in place it shakes and it makes this cracking kind of noise. and one time i was driving it and it wouldnt go past 20 no matter how far i pushed on the gas. and i pulled over and turned it off gave it a minute. and after this it was going faster but with a delay. other times it runs perfectly fine with no problems. and other times it wont go past 60 when on the free way, so you see its a real peoblem and it may cause an accident. so any help would be very appreciated.