I currently have 7 Cherokees(two 84z, an 87, a 96, a 99, a 2000, and my Beloved SilverStone Metallic 2001) that I all work on. From 84 until the end in 2001 they used vacuum for HVAC blending doors. From 84 until late 86 early 87 the vacuum canisters(two of them,.metal) were on the passenger side under the hood up on the wheelwell. From 87(first year of the 4.0,.maby the best year of the 4.0) until the last year of the Cherokee, 2001, the vacuum canister(plastic) is behind the front bumper on the passenger side. My 99 had the same idle problems you describe chevyboy14, and it did take a good, newer looking TPS from the Auto Salvage yard to fix it. I dont trust the quality of auto parts store sensors, and didnt want to fork out the Big Dough for a Chrysler TPS. I would only do that for my 2001.