01 surge with rough idle

Hello everyone, I need some help. Ive done some research but cant come up with a starting point. My truck developed a new rough idle and a surge while driving. It doesn't do it under load or acceleration. It is worse with the cruise control on. At idle the RPM's drop 50 to a 100 but not all the time. It occures more often when warm then cold. No power loss noticed but I can raise the engine RPM to around 1300 to 1400 and notice a fairly constant miss. I have recently replaced all the glow plugs right side harness, changed the oil and looked for oil in the ICP connection. Can someone let me know where to go next. I was thinking the IPM but don't know where it is or how to test.