Engine surge? Please help

Tonight I just replaced the thermostat in my 99 disco I. While I was letting it run, I ran my hand under the thermostat housing to check for leaks and kept bumping into the major wire harness that runs right under and in front of it. Each time I put some pressure on the harness the engine would surge as if I was playing with the throttle. What could this mean? Bad ground perhaps? Please help. This would correlate with a problem I have had lately. Upon warming up...at times while driving my engine will surge and I'll actually see the tach surge about 500r/min or so. It comes and goes.

Thanks for the help:confused:

Dave