I have a 1999 Honda accord Ex. 247,000 miles. I finally got around to changing the motor mounts the other day, and when I got it all done, the motor shakes pretty noticeably. I can feel it inside the car, and it wasn't there before I changed the mounts. (the old mounts were cracked). I was checking the computer with my OTC scan tool, and noticed the timing advance was jumping from 7 degrees, to 20 degrees, and for a split second, it jumped to something like 50 degrees, but then would immediately go back to 10-18 degrees. It feels like the motor is misfiring, but the scan tool didn't detect any, and there are no codes. I cleaned the intake, the IAC valve, and it has fairly new plugs/wires, cap, rotor, etc. As soon as the engine is revved up to about 1400, the vibration is gone, and the timing advance stays at 8 degrees, until I let off, and it goes back to idle where it jumps around. I'm at a loss. Any advice?