Ok so my 88' Cherokee 4 liter is giving me problems, when the engine is cold it will idle very low and stall out then once the engine gets up to operating temp it begins to idle very high and just keep getting higher and higher. I replaced the TPS sensor, the IAC sensor, cleaned the gunk off the little sensor that screws into the intake manifold, the one with 2 wires coming out of it, cleaned the throttle body and no hissing like a vacuum leak, dont know where to go from here, has anyone else had this problem before?
I've had it do that for numerous reasons. Adjust or test your TPS, the flat three pole connector. Check the ground first with an ohm meter, should be very little to zero resistance. Adjust 4.6-4.8 volts in and .8 volts out, if memeory serves me right. The out voltage goes up as the throttle is opened, with the connector connected for the test. I slice the wire insulation with a very sharp knife (lengthwise about 3/8 inch) and test right through the insulation to the wire after (main harness side) the connector. Run the wires over the intake rubber from the air box to the TB. You can reseal the cut with a dab of silicon.
If your ground is messed up, I will give you some tips later. There are some tricks I learned the hard way. The easiest solution is to run another ground wire to the chassis (firewall). But if that ground is screwed there are other sensors involved.
Re-tighten the manifold bolts, top and bottom, start from the center out. Be real careful of the end studs, they will snap off, but truthfully they really don't do much and if they do snap off it isn't the end of the world. I've run them for years (decades) with snapped off end studs.
You can plug off all the vacuum lines running to the manifold, for a test, except the fuel regulator and the MAP (at the TB). The vacuum line under the battery tray is a prime spot for rot, it runs to the vacuum canister behind the front bumper passengers side.
High idle is most often something to do with the TPS, or a vacuum leak.
If your MAP screws up it will usually idle really bad and when it does run, spew black soot out the exhaust.
Check the O2 wires where they run behind the power steering pump. They can cook on the exhaust manifold. About half the time someone has done top end work on the motor (or a water pump) they route the injector haness where it runs down the front of the motor wrong, to the knock sensor, engine temp. sensor and O2 sensor. It cooks where it is almost impossible to see.
