trublue

Hello,

I have a stock 1996 Jeep XJ, 4.0, AW4, 4WD. At idle, the tachometer is steady at 750 rpm, but I can feel a very intermittent miss/stutter. No CEL., and no instances of misfires reported on a OBD-II reader. I later found out that these engines have to record a certain number of misfires in a specific time period to record it as "not normal". I also feel a mild shudder/vibration like something is loose as soon as I accelerate from idle to about 1000/1200 rpm, and then it smooths out. I suspect these two symptoms are related. New plugs,new plug wires, new rotor, etc. I suspected engine mounts, but they looked fine. A local independent shop inspected it, and could not find anything wrong, and admitted that without a code they would be replacing parts blindly. The local Jeep dealer suggested a BGK top end cleaning. I could see that helping the miss but not necessarily the shudder, unless I had a lot of carbon buildup.

Would slightly worn engine mounts or transmission mounts allow such a vibration over a certain rpm range? IAC or some other sensor? Minor vacuum leak?
Engine accessory?

It is definitely in the engine, as I can shift the transmission to neutral and feel the same shudder over that range.

Thanks in advance

dzywicki

What brand of plugs did you use? I didn't think it mattered much until I chased a warm idle miss for months. I had replaced the plugs with Autolite and didn't think plugs would maker it do that. Went back to the champion coppers and everything was great at idle again. Best part was it started instantly, idled great, had some other parts cleaned and checked etc. I have 2 XJs and a YJ. Only champion coppers for me now.

If you are already using Champion plugs then I got nothing.

trublue

At present I am using a set of Accel plugs (from the Jeep Accel tune up kit purchased on Amazon). I will try some Champion Coopers since it is such a cheap maintenance item. From the champion website, it looks like Champion 412's (RC12LYC) are the ones for the 4.0.

https://www.championautoparts.com/Fi...eep%7ECherokee

Thanks for the suggestion.