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Hello, I’m very new to the forums and this is my first post. I have a ‘99 XJ 4.0 and the previous owner has cut into some wires on one of the sensors and I have no idea what it is. I’ve been having an issue with my Jeep where it will lurch and the rpm’s will shoot up when I hit bumps and sometimes when I’m just driving normally. It doesn’t do it all the time and it’s mainly when I’m hitting rough spots on the road. Every once in awhile it will die at a red light also. It’s throwing a P1391 code occasionally but it goes away within a day or so. I’ve replaced my TPS very recently and didn’t fix the issue. If anybody could please give me some insight on what this might be I would greatly appreciate it.
Thank you! Do you think this could be the source of my problems?
I think so.
The IAC isn't a sensor, it's a small actuator that controls air during idle and low load.
It bypasses the throttle body (because it needs to flow only a small amount of air during idle, much smaller than the throttle body can control) so if it turns on when it should not, I imagine it could increase RPMs at any load (not in front of the Jeep st the moment, so others should correct me if I'm wrong)
If it shuts off when it should not, then it could cause you to stall or cause RPMs to be erratic at low loads (at a stoplight).
I'd say fix it - it's likely at least part of the cause of your issues. It definitely would make me sleep better to replace and repair that wiring regardless. It'll cause a problem eventually.
If you replace the IAC itself remember you might need to adjust the new one. It's not hard. Lots of guides and instructions online. There also should be a little sheet of paper in the box telling you how to do it. It might need you to take it out and adjust and reinstall once or twice if you get it way wrong. If it's adjusted wrong it is obvious (either stalls or RPMs are very high at idle).
EDIT
In the short term if you are plant on replacing the harness, maybe replace the wire nuts with automotive wire crimps/ connections. That will be 100 times better than the wire nut as long as the only issue is the wire nuts (and not incorrect wiring).
Last edited by moonsandals; May 31, 2020 at 12:22 PM.
I am noticing that a P1391 looks like a Crankshaft or Camshaft positioning sensor thing.
So I am going with a no.
I don't have much experience with this but usually the high idle problems that guys sometimes
experience is caused by the IAC.
Regardless that needs to be corrected.
I am noticing that a P1391 looks like a Crankshaft or Camshaft positioning sensor thing.
So I am going with a no.
I don't have much experience with this but usually the high idle problems that guys sometimes
experience is caused by the IAC.
Regardless that needs to be corrected.
I missed that there was a code - good catch. I agree that the CPS should be checked.
I know the typical IAC symptoms are high idle, but I thought that's usually bdue to poor adjustment or a leak. This is a whole can of worms because of the wiring and I figured was more of an intermittent isse, maybe similar to an intake leak. Definitely doesn't fit into "typical" issue territory. Fun!
I wonder how the CPS harness looks if the previous owner did this to the IAC
I think so.
The IAC isn't a sensor, it's a small actuator that controls air during idle and low load.
It bypasses the throttle body (because it needs to flow only a small amount of air during idle, much smaller than the throttle body can control) so if it turns on when it should not, I imagine it could increase RPMs at any load (not in front of the Jeep st the moment, so others should correct me if I'm wrong)
If it shuts off when it should not, then it could cause you to stall or cause RPMs to be erratic at low loads (at a stoplight).
I'd say fix it - it's likely at least part of the cause of your issues. It definitely would make me sleep better to replace and repair that wiring regardless. It'll cause a problem eventually.
If you replace the IAC itself remember you might need to adjust the new one. It's not hard. Lots of guides and instructions online. There also should be a little sheet of paper in the box telling you how to do it. It might need you to take it out and adjust and reinstall once or twice if you get it way wrong. If it's adjusted wrong it is obvious (either stalls or RPMs are very high at idle).
EDIT
In the short term if you are plant on replacing the harness, maybe replace the wire nuts with automotive wire crimps/ connections. That will be 100 times better than the wire nut as long as the only issue is the wire nuts (and not incorrect wiring).
Thank you so much for your help I greatly appreciate it. I’ll have some time to work on the jeep tomorrow so I’ll keep y’all posted and let you know how it goes!
What sensor is this??
