Tractor Repair: Engine Surge at idle, fuel hoses, pump fuel

Question
I have a case IH 5130.  It surges at an idle 800-1000RPM.  I have
replaced the fuel pickup pump, fuel filters, air filter, and made sure the
return line is not clogged.  The tractor has been like this for awhile.  The
fuel pump stopped working is why I replaced it.  I am retired Army
maintenance background.  I have always fix my owning stuff but this one
has me scratching my head.  

Answer
 These tractors are notorious for fuel lines cracking between the fuel tank and lift pump, causing air to get into the fuel system.  It usually causes a problem starting the engine after it has sat overnight or for a couple of days because of fuel draining back to the tank.  I have also seen it cause a problem similar to yours, so you might want to check the rubber fuel hoses from the engine to the tank, and also on top of the tank under the cab or platform.  Otherwise it may be a problem with the governor in the injection pump.