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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
My 1988 Jeep XJ with a 4.0 is acting up. Most of the time it starts up, on startup it goes to 2k rpm and then idles right down to 800 or so. Which I believe is all good and normal. Sometimes it goes all the way up to 2.5k rpm and rev hangs and slowly drops down to a high idle (1000 to 1200rpm). Other times it starts up and shoots up to 3k rpm and refuses to idle down until I shut off the car and re start it. After I re start the engine, it goes up to 2.5k rpm and rev hangs but not as bad, kind of just does a bad job of idling down smoothly and quickly. Also, when I turn on the AC, the IAC never once has compensated for the AC, it just bogs down the engine about 200-300rpm, doesn't idle up or compensate whatsoever. I'm not sure if it is supposed to compensate but it would make sense that it should. I have unplugged the IAC and tested how the AC affects idle and it does the exact same thing as when its plugged in. Absolutely nothing. Is this my TPS or IAC or some other problem? I know it could be that the IAC is already letting as much air in as possible, therefore it cannot compensate for AC but I'm really not sure. I have cleaned the dipstick ground and replaced it with a stainless steel bolt and stainless steel washers, made sure it was super clean and still tight a few days later. The IAC is also very clean, always has been since I bought the jeep around 6 months ago. Regardless, I have cleaned it a few times. Most of my electrical has been cleaned too, including the C101 connector. My throttle body is also pretty clean. Any Ideas?
Here's some things I have done:
- Replaced, went back and checked adjustments of TPS (NTK)
- O2 sensor (NGK)
- Most vacuum lines
- Distributor rotor (napa)
- rotor cap (napa)
- spark plugs (NGK)
- spark plug wires (Belden)
- cleaned the IAT
- cleaned IAC 3 times
- cleaned C101 3 times
Can you provide an Ohms reading from the "B" terminal (back probing) of the TPS connector and the negative post of the battery?
it's absolutely all over the place, it started at 10ohms and when i wiggled the wiring harness by the map sensor, it shot up and was just absolutely going crazy into the 60-70 ohms area. If i position it i can get it lower than 10 but obviously thats not gonna stay there...
You need to peel back the wrapping on the wire looms and find the splices. It is possible that you can get away with just fixing one, but there could be two that are suspect. The diagram shows two, but mine was one large one. The splices are literally held together with a metal crimp that looks like it should be on a pigeon's foot, wrapped in grey duct tape. They need to be properly soldered together, which can be easier said than done, but it will make a big difference in drivability and dependability. The circuit is the one highlighted in yellow. The wagon wheels are the splices. If you follow the TPS wires into the loom, you will eventually run into the splice(s).
You need to peel back the wrapping on the wire looms and find the splices. It is possible that you can get away with just fixing one, but there could be two that are suspect. The diagram shows two, but mine was one large one. The splices are literally held together with a metal crimp that looks like it should be on a pigeon's foot, wrapped in grey duct tape. They need to be properly soldered together, which can be easier said than done, but it will make a big difference in drivability and dependability. The circuit is the one highlighted in yellow. The wagon wheels are the splices. If you follow the TPS wires into the loom, you will eventually run into the splice(s).
alright, thank you very much! I'm going to start this tomorrow, hopefully it goes well, wish me luck, ill update on how it went and post photos of how i did it.
That ground splice looks to be in excellent condition. There is another one with a 90-degree bend in it. That one is interesting, it appears to be different wire, but still brown and white. Does that continue to the C101 connector, or does it continue into the loom? I suppose it is possible that you had a poor contact while back-probing the "B" terminal of the TPS connector while you were checking the ground. Does the idle settle in as desired right now that the ground is showing low Ohms?
That ground splice looks to be in excellent condition. There is another one with a 90-degree bend in it. That one is interesting, it appears to be different wire, but still brown and white. Does that continue to the C101 connector, or does it continue into the loom? I suppose it is possible that you had a poor contact while back-probing the "B" terminal of the TPS connector while you were checking the ground. Does the idle settle in as desired right now that the ground is showing low Ohms?
it actually bypasses the c101 connector, the brown and white wire is cut on the c101 connector itself and the wire jumps across the connector to the other loom to bypass it.
its been fine so far, If it continues to get stuck at high rpm and hang sometimes could that be the IAC not responding or something?
I had the exact symptoms you have. I made a mistake of fixing two things at once, so I'm not entirely sure which one was the fix. I initially bought and intended to install an NOS MOPAR TPS. While I was in the process of replacing the TPS, I identified that my ground had drifted up to 6 Ohms. I first fixed the ground and installed the MOPAR TPS. The idle has been good ever since. I was hoping to validate it was the ground and not the MOPAR TPS when you fixed your ground. That was cleaver of the PO to just bypass the ground through the C101. If you continue to have the problem, maybe an NOS MOPAR TPS is in your future.
06-28-2024, 03:25 PM
Intermittent idle problems
