I traded for a 2000 f350 6-speed the other day. The guy indicated that he had a new set of glow plugs but they needed to be installed. So after checking the relay to make sure, I went ahead and changed them out tonight. Now it starts great but it's running really rough. Almost like its only running on half of the cylinders. I'm sure I plugged everything back up. All I had to disconnect was the main plug on the drivers side valve cover, and the 2 plugs attached to the dip stick bracket going to the a/c and the rubber line going from the intake to the sensor module thing near the heater hoses on the passenger side. I re-installed everything so the only other thing I can think of is maybe I bumped some other sensor or something causing the rough idle.