I have a 91 318is, I filled up gas the other day at work and i notice that the car starts to sputter, when accelerating. It loses power in certain rpms and then shoots back up and then starts to lose power and sputter again. Now it has gotten worse and has just started to sputter and lose power throughout the whole rpm band. It also now idles really rough. When idling the rpms keep going down like its about to turn off and then it goes back up. The muffler is also making weird sounds as if something is popping sometimes when accelerating. Does anyone have any idea what this could be? I thought it would be fuel related, or vaccuum leak. My friend tells me its just the spark plugs. Im stuck at work for a couple of days and im not going to be able to take it to a mechanic for a little while so i can feel it getting progressively worse as i drive it. Any help or advice will be greatly appreciated.