i have a 1986 528e, yesterday the car was running ok, this morning upon starting the engine started shaking and i could hear the engine misfiring, upon driving acceleration is hard but car will reach speed, the engine shakes a little more in the 75-80+ mph range on hwy. When i turn car off i can smell a "burnt" exhaust smell insted of no smell at all. i changed fuel filter and upon trying to blow through it could not, i gues it was clogged pretty good. the car has a fairly new fuel pressure reg and i changed spark plugs in June. Any ideas on what to check or do ? I don't want to spend a ton of money when the problem may something simple.