Ok to start off with it is a 94 MM that I just purchased with a 2.4 EFI M/T that did not come with factory A/C obviously and I am going crazy trying to fix this thing. I got all the parts from a donor truck that was near the same year, same motor and tranny. I also have a 91 MM that came with factory air (show truck) that I used as my go to so to say for help with the install. Ok now the problem is IDLE and gas mileage but I will get to that shortly. The only thing the donor truck did not come with is the coolant temperature sensor on the side of the thermo housing that the a/c harness plugs into. I did not realize this till I got everything installed and charged and the a/c would not ingage. Checked the show truck, noticed sensor, robbed sensor, installed and a/c worked like a champ but the idle went crazy as soon as I plugged the sensor in. Not long after the CEL came on. Checked code and it was the engine coolant temperature sensor. Replaced the one on top of the thermo housing and the one on the side that the a/c harness is hooked to and still no dice. I have either replaced or swapped for a known good part the... IAC, motor position sensor, idle control servo, EGR, PCV valve, both temp sensors, TPS sensor (also checked its setting and its voltage output to spec in manual and its in range), ECU from the show truck and the donor truck, MAF, a/c controller under dash, checked idle set screw. The CEL is now off but still idling like butt due to replacement of the temp sensor. When I purchased the truck it averaged 23 mpg or so and that has went to around 18 or worse.
If I unplug the harness (the 5 wire one) on the throttle body that would be the IAC, it idles fine. If I unplug the temp sensor that is connected to the a/c it idles fine but no a/c. The idle is all over the place, just steady up and down and pretty high not sure of RPM but I would say a little above where it should be when the a/c is engaged judging from my show truck.
The things I haven't gotten to are the O2 sensor and the cat converter. I also noticed a small crack where the pcv valve screws in, not sure but dont think thats my idle problem. Also checked all vaccum for leaks and also the head and throttle.
This has got to be electrical somehow I think but I don't know. ANY help at all would be greatly appreciated. Thank you in advance!!!!