Good day to you all. My 89 740 GL Wagon has started giving me some slight, but growing, engine problems in the last month and week. It's winter here and I've been leaving it outside - I've seen my MPG drop from 22 to 19 or worse recently, and I'm not idling it THAT much. The engine still runs ok, doesn't cut out, but it seems a bit sluggish and has gotten noticeably louder and more grumbly. What really got me concerned is that last week, after getting off a short highway run, I began to hear a sound in between gears or whenenver its at high RPM and I release the accelerator. It isn't that lound, but sounds like some sort of rattling backfire, like in a tin can. I checked for backfire at idle by checking for suction at the tail pipe, it was ok. I'm probably going to take it in, but I'm still hoping it might be something simple I can do. Any pointers or suggestions greatly appreciated.