I have a 92 lerado with 4.0 that has 200k, this is my first jeep so I dont know all the tricks. when I got it it ran rough, the other owner said he has not done anything to it in a year , so I thought a simple tune up would fix'er up .... NOT. heres what i have done so far.
new cap & rotor
new plug wires
new plugs(champion coppers)
new air filter
1 new injector.
I have cleaned the throttle body (off car) also cleaned the IAC, the reason for the injecter (the one under the throtle cable bracket) I pulled the connector to them while it was running and that one was the only one that DID NOT make a change in idle....
so at idle she's run very poor, rpm seem ok @ 700 or so but very rough, when i drive it and get into the rpm's like 1500 or higher it runs fine... any help would be appreciated... Thanks

 

Yeah I have the same problem on my '91 Laredo with 185k miles and have yet to discover a solution. My next thing I'm going to try is the timing...

 

Have you tested the TPS for correct voltages and operation? Checked for vacuum leaks?

 

Check compression and leak down. And see what you get.
pull the valve cover and make sure everything is good under there.
might have to pull the head and check the lifters.