I took mine apart about a month ago and cleaned it by hand. There was some carbon build up on the underside of the butterfly or flap and all over the IAC. I sprayed and cleaned the IAC also. It did seam to help a little but the idle is still low or at least i feel like it is. It idles right under the 500rpm notch. I might change the IAC soon to see if that helps. I already did spark plug changes, new fuel injector seals, new number 3 injector, oil is fine other than the leak. I have always suspected a vaccum leak somewhere but have yet to find it.

 

as for the vacuum, they have a tester out thats called a smoker test or some ****..it fills the engine with smoke so you can find any hard to see leak..

 

Has anyone found the problem yet?? My wifes ZJ 4.0 has been doing some of the same stuff (hesitating/cutting out at stops and corners and sometimes really hard to start). I changed the IAC and the fuel pump and both seemed to help but no completely solve.

My latest theory is a leaking intake manifold. Its always had a random #6 misfire and I resently remembered that the PO broke the last bolt hole on the back side of the manifold. I'm thinking that might be the reason for all the random weirdness of this ZJ. Anyone encounter this?

 

I have the same problem! did replacing the IAC Valve fix it?