The first thing I would consider is that the EGR valve is not closing completely when it gets hot. So I would remove and thoroughly clean the deposits out of the EGR valve. After that, try manually opening and releasing the valve; it should close easily and completely every time. If it does not close consistently, the EGR valve should be replaced.
After having been driven that many miles, it is also likely that fit of the valve stems in the cylinder head valve guides has become loose. When that happens; air can be sucked in to the intake manifold through the valve guides. Loose valve guides will in that way cause the air fuel mixture to become diluted. Loose guides will also result in inconsistent valve sealing, which causes the cylinder compression to drop. And both of those things can create increased or unstable idle speeds.
There is one other possible cause for this problem: Today's gasolines contain chemicals which produce heavy carbon deposits on valve stems. This can prevent valves from closing consistently or completely. So it might be worthwhile to add a full bottle of Chevron Techron fuel injection and combustion chamber cleaner to the fuel tank just before filling it with fuel. This product often takes 50 to 75 miles of driving to do its work. But the results are better than other products of that type.
I tried all the things suggested and the problem persisted on my 91 Jeep Cherokee. I was about to give up on it and just beginning to really get used to driving that way.
I then notice about half the exhaust manifold bolts were loose and tightened them to the proper torque settings which somehow cured the high idle problem.
I have no idea how this could be connected, but it is something others can try if the problem cannot be resolved in the proper manner.
hey i found this on another forum it's a cherokee but i hope it helps good luck