My '96 328i was running rough on the freeway. The RPM's were not moving but the needle that show the gas mileage was jumping from 40 to 10 and back. It quickly went lower until I exited and pulled in a gas station where it stalled. My gas guage showed 1/4 of a tank but after I filled it with gas, it started and I was able to drive it home. Can anyone help me narrow it down?