I recently purchased a 91 560 SEL. It has 200k miles. When you crank it up it idles smoothly for about 30 seconds then starts to stumble down then pick back up. When you drive it you feel the same miss even at cruising speeds. If you stomp on the car it will hesitate then take off like nothing is wrong--but once the rpms start coming back down it will start to miss immediately. I have run some fuel conditioner and super unleaded fuel, changed the plugs and wires, but the miss is still there. I plan to change the fuel filter next and look for vacuum leaks...any ideas out there???? Thanks in advance for any help!!!