My 97 Cherokee with a 4.0 has been a terror lately with a very inconsistent issue. The problem seems to be worse in cooler/cold weather 60 degrees or less. Initial startup the engine will occasionally (more times than not) run rough with a hunting idle or a consistently high idle, sometimes while idling in park the engine will actually die and need full throttle to get it to restart. If it doesn’t stall while idling in park usually when I put it in reverse/drive the rpm’s will drop and the engine will die. I can nurse it along and get going, while driving it usually runs fine but also “occasionally” has what feels like a misfire or loss of power. The main issue is at idle, it smells it is running rich, sometimes will smoke while spitting and sputtering. Things I’ve done, new IAC, TPS, Coolant Temp sensor, upstream o2 sensor, MAP sensor, completely removed throttle body and cleaned multiple times. Recently did new exhaust manifold so it has a new intake/exhaust gasket, new PVC/CCV, cleaned all of my grounds. I have searched high and low for vacuum leaks with no luck, I’ve started checking the wiring harness and I have not found anything yet. Only code for CEL is a transmission code. I’m sure I’m forgetting something else I’ve done as well.

What method are you using to search for vacuum leaks?

Any trouble codes?

I’m using carb cleaner to sprain around any connections. That’s how I found the intake was leaking around the gasket, the same problem continued after repairing that though. I have one code for the transmission.

what story do the spark plugs tell?

i replaced them over the winter, forgot to mention that. At that time they looked decent, I should pull them again just to see. Maybe today, I’ve never used a mopar TPS and I know everyone says it makes a difference. I’ve tried multiple other brands and I’ve had the same issue every time. I just figured I’d see some other ideas before I throw more money and parts at it.

Have you tried shaking the connections/wiring harnesses?
Its an "Old Guy" method of diagnosis for when the Parts Cannon is empty, and you aren't sure of how to diagnose via electronic testers, or if they aren't available.
The Old School way, of starting it, running it at idle, and grabbing a wired loom or part connector, and giving it a jiggle, (NOT a FULL pull/break it style) might sometimes help.
Especially the loom of wires that goes across the top back of the firewall. Wires tend to fray and rub, and are hard to find without extensive electrical work.
Although you can test and test properly and get exact results, sometimes, putting on a rubber or leather glove, idling the engine, and shaking some contact points or wire looms can, at least, clue you in to where the problem lies.

Either way, it costs you nothing but some time. When you shake something, and it stutters, youve found your issue.

Please always wear a leather glove, or rubber mechanic glove. Those plug wires and coil have some juice.

Shake/tShake/Manipulate/Jiggle all connections and harnesses...
LISTEN for a CHANGE.

Again, Costs Nothing... finding the problem is Priceless.



Good Luck, God Bless.

It’s funny you mention this method, last night I was doing exactly that. Not very extensive because I was short on time, I will try again. What makes this method difficult is that sometimes the thing can sit there and idle perfectly and without even touching anything the idle will get crazy for a few seconds then correct itself. Other times it will just sit there with a high idle and stumble/stutter on its own without me touching anything. I’ll be sure to take a thorough look at all of the wires. Thank you!

Throttle Body is the Issue, I took mine apart and cleaned it put it back together and it cured the problem for a while but,now it is starting up again so what I'm going to do is Buy a Brand new Throttle Body along with sensors and Install it, I believe this Ethanol Gas we are using is The Culprit and is Gunking Everything up, Just my Thoughts. Going to Try it soon hope this Helps.

I did this not too long ago, it did seem better but for a very short period of time. Maybe a day then it started doing the same thing. What makes this issue difficult for me is the fact that I can drive to work occasionally and it will run perfectly, go to leave work or wherever and boom it’s acting up again. Very consistent but also not consistent issue I’m having.

while messing around today I found that the shaft/seal on the throttle body for the butterfly seems to have some excessive play. For testing reasons I removed the shaft and put grease on the seal and the Jeep has been running perfectly. I know this isn’t the correct fix, is there anyone that sells a throttle body rebuild kit with seals and bearings? Or will I have to go all new throttle body?

Recently I replaced my IAC and noticed the little rubber O ring gasket on my old one is deformed. Long story short, it must have been a heckuva vacuum leak because not only did my idle become more regular but immediately acceleration was much sharper. Now that one would be a devil to hunt down, I recommend making sure you have that new O ring installed

that’s a good point, it was on and I even slightly lubed it prior to install so that should be good

On may not be good enough. They get munched once they're installed. They're one and done. Again I couldn't believe the difference mine made

Not only that but as the O2 sensor reports the less lean mixture the pcm seems to pull timing over the course of a week or so too.

Your issue sounds very similar to an issue I struggled with for a while. I changed a bunch of similar parts to no avail and scoured the forms for a solution. After a process of elimination I was able to narrow it down to the CPS (Crank Shaft Position Sensor). Its a pretty easy fix taking less than 30 mins and costing around $20-$60. Good luck, hope it helps!