I have a 95 GMC 2500 that will occasionally surge at idle. I never noticed the problem until I recently had broken manifolds that I had changed out. At the same time I replaced the fuel filter, air filter, put in new spark plugs, new cap, new rotor, new spark plug wires, new heater core and a new thermostat. Then I started noticing the surging. I replaced the injectors (they needed it) when that didn't fix the problem I replaced the EGR Solenoid, that didn't fix it. Next was the EGR Valve which didn't change anything. I pulled the Idle Control Motor and it looked good but is next on my list of things to try.
The surging comes at random times. Sometimes I drive the truck cold and it happens, other times it doesn't surge until it has been run and warmed up. It does seem to happen more frequently when I have run the truck until it warms up then I turn it off and start it a few minutes later but even that is not 100% of the time. I don't notice any problem while driving it until it idles. One time in the last few weeks since it started I had it in park and when I put it into gear the RPM's dropped and it died but that has only happened once. At this point I am out of ideas. I'm hoping that somebody on here has an idea.
The surging comes at random times. Sometimes I drive the truck cold and it happens, other times it doesn't surge until it has been run and warmed up. It does seem to happen more frequently when I have run the truck until it warms up then I turn it off and start it a few minutes later but even that is not 100% of the time. I don't notice any problem while driving it until it idles. One time in the last few weeks since it started I had it in park and when I put it into gear the RPM's dropped and it died but that has only happened once. At this point I am out of ideas. I'm hoping that somebody on here has an idea.