My 96 Ranger 4.0 5spd 4X4 has been to the dealer and had the following: new water temp sensor, throttle body cleaned, new IACV, reprogrammed the computer. I have owned it 7 months (2nd owner)
On 3 out of 7 days it will stay at 1800-1900 on cold starts for 10 minutes or more while driving. It will not come down when I stop at a stop sign, but will slowly creep down if I have to stop at a red light. If it eventually comes down, it will not go back to 18-1900 until the next cold start. The rest of the time, it will not idle below 1400 until the truck has come to a complete stop. If I knock it out of gear and just coast from highway speed, the engine will not drop to normal idle until I come to a full stop. The 2 times that I have removed the battery cable to clear the computer has provided me with what I feel is a normal condition.--The engine idle will drop down fairly quickly to a normal curb idle when slowing down for a stop, or when coasting at highway speed to see what results I obtain.
But this normal condition will only exist for 5-10 minutes, then it goes back to the sticking at 1400 thing. This is very annoying when driving in stop and go traffic, or when driving in neighborhoods. It has been to the dealer too many times lately for this with no results.
I'm not sure if they have fully experinced these problems or not. The last time the tech rode with me, I was told that the computer pretty much is doing its thing, and that they could not do anything. I know this is not true, because I have seen the idle behave properly at times.
Anyone got any ideas on what I should look for?

 

Have you checked for vacuum leaks? I know there is a common area that leaks on the 4.0 but I can't recall the location, check with wptski.

 

Like Ken suggested, I had a similiar problem on my 97 Ranger 4.0L. My idled at about 1800rpm when warm just before I fixed it. I cleaned the MAF three times, cleaned the throttle body, replaced the IAC valve and the PCM too.

After chasing my tail for a couple months and knowing that there was a TSB on the gasket under the fuel rail. I took some Quick Start and sprayed it around the fuel rail near the front end, passenger side which is about the only place that it's really open and the engine reved up. That happened to be exactly where the gasket was broken and sucked into the first paired ports! About $12 for the gasket or that might be for the "O" ring type in the upper intake too.

Before a certain year, there was a gasket on top of the rail also which was eliminated.

I forget but did you say that you were a DTC(check engine light) code also? I was getting a Lean System code for both banks on mine.

They only give a mechanic two hours to edo that job! It took me a 30 minutes just to scrap the gasket off!!!