1999 Jeep Cherokee

OK so tell me what have you checked at this point? I see a list of parts that you have replaced and correct me if I am wrong but I understand that you replaced the cap, rotor, wires, plugs, idle speed motor, and throttle position sensor? Have tested the TPS to see if it is reading right? Have you checked the coolant temp sensor? How does the air filter look? Do you have a digital mutli meter so we can do a couple of test? Get back to me and we will go from there.

Ok you will need a digital multi meter, it don't need to be anything real expensive just one that works and has volts and ohm's. Once you have it I need you to unplug the coolant temp sensor and do an ohms test on the sensor (not the wire harness). Get back to me with the ohm's reading and if you do the temp when the jeep is cold then the temp at the time of the test too. Get back with that and we will test the tps next if needed.

Well the best I can find it looks like it is out of range, therefore I would replace it. Let me know how it goes.

Ok here is how it works. The coolant temp sensor provides information to the computer. With that information the computer will calculate injector pulse time and ignition timing. So when the Jeep is cold it causes a slightly richer fuel mix and higher idle. When it tells the computer the Jeep is at operating temp then the computer goes into what is called closed loop and with that it will use engine temp along with the map sensor and tps and cam and crank sensors to determine timing and fuel richness and injector pulse time. If the Jeep thinks it is colder then it really is this won't happen and it will use fixed information to try and run as it should.

Ok before I can walk you through any tests I need to know is it a Grand Cherokee or just a standard Cherokee and what is the 8th digit of the vin? Get back to me so I look up some tests. I would like to check the TPS and then the MAP Sensor. If it is the Grand Cherokee have you changed the fuel filter? Get back to me.

Being that you have a standard cherokee then you have no fuel filter so I can't ask you to change that. My 99 Jeep is a Grand Cherokee with the 4.0 and it is great. The Grand Cherokee is the only one with a fuel filter in the whole Chrysler family strange. Any how I need you to test the TPS first and let see what it is doing and that it is opperating right. First I need you to back probe the Orange wire with a paper clip or something then hook up your multi meter set it on the 20 volt scale now with key on engine off what voltage is there? Should be 5 volts now turn key off. If this is good then back probe the orange wire with the dark blue stipe and now with key on engine off, set on the 20 volt scale you should see about.8 volts now slowly lift the throttle the voltage should increase steadly with no drops or glitches and then at wide open throttle should read 4.5 to 5 volts. Let me know how it goes if this is good then we will check the map sensor and cam an crank sensor too. Get back to me.