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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.
Check the voltage across the IAC. The factory service manual will tell you what it should be. As an aside, my device doesn't show a real time IAC and I am not sure if they do unless they are the expensive ones they have in a shop. The IAC only really controls airflow and this should relate to short term fuel trim, in other words if it is slow to react the vehicle will stay lean (+ %) if the valve stays open and rich if it stays closed (- %). This condition will be reflected in you MAP sensor reading though and the pressures should spike accordingly. If there aren't large swings in fuel trim then it's definitely a mechanical issue.
The other thing you might want to keep an eye on is the TPS, mine reads 18 to 18.4% at idle. If I remember from previous discussions, the TPS on the AW4 Cherokees is tied into shifting, but I may be wrong.
Watch Schrodinger's Cat on YouTube, he does a great job of explaining how sensors work. Videos are long but worth it.
Scanned it again this this morning for a bit. Idled fine for about 10 minutes with no Long Term Fuel Trim values showing at all. Starts idling around 1000 rpm and back down to about 750 as it comes up to temp. Engine temp and intake temp seemed to come up to what appears to be normal. Throttle position stayed around 13 percent. After the 10 minutes I gave it a little gas and let it go back to idle (still in park) and the idle instantly went low to about 500 and was trying to stall out. It goes back to that with no pressure on the throttle. With the least pressure I can put on the gas pedal it idles around 600-650. I took pics of all the readings while doing this. Also Long Term Fuel Trim didn’t show until I initially bumped the throttle.
For information purposes it was 35 degrees outside at this time (if that matters on intake temp).
I’m going to drive it in a little bit and watch the live feed also.
Last edited by nitrousjunky; 01-16-2019 at 09:17 AM.
All of those values seem reasonable (I see mine everyday - with a digital dashboard). Nothing is jumping out. With all of the details you've provided, i'm apt to suspect the IAC mostly (one that is not opening when it is warm). Either a problem with the controller itself (most common) or a problem with the wiring to the controller (not as common - but happens). So you can throw a part at it, or dig deeper into diagnosing the voltage on the controller based on what the specs should be (which I don't know off the top of my head).
It sounds like the IAC, but I find it odd that you aren't seeing swings in STFT. I should add that I had similar symptoms when my MAP went. The pressures kept on spiking even though I wasn't touching the throttle, but I was getting an extreme rich condition from it (If I remember, almost -25% (rich) spikes in STFT. I have to look back in my notes). Make sure you pick up a Mopar IAC and report back.
In my experience an OEM Mopar IAC is not necessary. It is not a sensor, and the aftermarket one I have in has given me 2+ years and 40k miles with no issues (Standard Motor Product - but I avoid their "T" product line). But do what you think is best for your needs.
IAC doesn't have a lot to do with fuel trims. Fuel trims are primarily a MAP, O2 Sensor, and temperature thing (Engine Coolant Temperature sensor and Intake Air Temperature sensor). With MAP and O2 being the ones that can really throw the values off.
01-12-2019, 08:45 AM
Fixed
