Idle problem on 89' XJ

Ok bear with me I am coming to you guys for an answer because I am lost. I am a mechanic and this one has me lost!!!!
For about the last month my 89 XJ has been surging while driving. It is an 4.0, 4x4, Automatic. I replaced the plugs, cap, rotor, wires and fuel filter. I cleaned the K&N filter and oiled it. I cleaned the throttle body plate due to carbon build up. At that time the idle started getting worse. At a stop in gear or not it will idle real eratic. Anywhere from 800rpms to 3000rpms. I then cleaned the AIC valve and replaced the TPS. This helped very little. It doesnt seem to be jumping as high but still idles around 1500-1800rpms. I also replaced the MAP sensor. This particular cherokee does not have a mass air flow sensor from the factory and the EGR vavle has been disconnected for as long as I can remember. The engine only has about 15,000 miles on rebuild and has given me no problems till now. Any ideas would be greatly appreciated. :gonnablow

check your intake bolts . mine were loose& tightening them solved my high idle problem

Well I checked the Intake bolts they were tight. After talking to my brother-in-law which is also a mechanic he told me to start my Jeep and take the air intake off the throttle body. He said with it idling to put my finger over the IAC hole on top of the throttle body. He said it should stall the engine. It didn't. He told me the next logical thing would be to replace the IAC vavle. I did and everything is back to normal. I hate that you cant plug these older XJ's into a scanner and find out whats wrong the first time. I now have spent $175.00 in two days to fix something that should only have cost me $75.00. So hopefully this thread will help someone in the future from spending too much money.