My 90 Cherokee is all stock, relatively low miles 120K, I've gone through a few issues already and replaced a good amount of parts, but one issue that still lingers is the random stumble at 65+mph. Usually on a cold start I've run it for about 45 min @ 65+ no issues but, after parking, and letting it sit for a couple hours, then return home I'll get some hesitation or stumble around 65mph. If I let up on the throttle and poke along at 55 it seems to go away. If I get on the throttle right after it happens, I still have power and seems ok for a bit, but will stumble again while cruising. I replaced the TPS, coil, distributor, plugs, wires, connector refresh, ground checks, chasing this down, but no change. I'm thinking its possibly the fuel pump, since it seems to grumble sometimes at idle and makes a whirring jet noise when hot, but it was replaced about a year ago, not sure the brand. I don't want to spend anymore money chasing this down, so any advice from the experts would be appreciated!

 

This may be miles wide of the mark but when I had fuel pump issues it turned out to be a kinked fuel line. I replaced the pump twice trying to solve grinding noises and poor running but one of the lines up front was kinked enough to cause an obstruction.

It's an outside chance but it won't cost anything to have a look.

 

Did you ADJUST the new TPS on the Engine side?

 

It was actually idling and running just fine so I left it alone till now. I just adjusted it and restarted it, the idle was high so loosened the bolts to adjust again (per your link instructions) and the top bolt broke off while loosening and now the bottom bolt is stripped. I think someone has messed with this TPS before me. Getting a new top bolt isn't a problem, fixing the stripped lower hole will be. Looks like I have to remove the throttle body and re thread.

 

Finally was able to fix the bolts and adjust the TPS for the engine settings, no change in hesitation/stumble at 60-65. Seems to happen so quick and randomly I have a hard time telling whats going on. Any other suggestions?

 

Put a new fuel pump relay in it or just move all the relays down one position and see what happens.

 

No change moving the relays. I did notice the hesitation at a lower speed today (45mph), still at light throttle though. Was only a few minutes after starting so maybe not a heat issue either. Now I'm wondering if its a overdrive/4th gear problem? RPM seems to jump down, then back up, but only during light throttle. I shifted from D to 3rd and no issue.

 

Can you see the tach needle drop when it happens?

 

Yes, it's pretty quick when it happens, but seems to drop about 500 rpm.

 

I just resolved an issue like this today with my 90 MJ.

But, I never saw the tach drop. Felt like a quick clunk in the drivetrain leaving a stop and at light throttle at cruise. Intermittent.

I refreshed the coil/ICM connections. Didn't work. Replaced just the coil with a spare. Seemed better. Kept that coil and installed a used ICM and it hasn't happened again.

 

I had a similar thought previously, I have two ICM and two coils, I thought something changed initially, but after driving 50 or so miles, problem happened again. neither variation of either ICM or coil made a difference.

 

Okay. Just throwing it out there. Like I said, my RPMs never changed.

 

Been driving it more lately and have been able to get a better idea of this random hesitation. Sometimes it seems to go into overdrive real quick then drop back out. Other times it will be in overdrive and drop out and then go back in a couple seconds later. I've also noticed this happening in lower speeds around 35-40 as well. I read in some other posts that the brake switch can cause the torque converter to disengage. Just to see if it was related I tested it. I stayed on the gas at about 65mph and rather than stepping on the pedal, I just lightly kicked the side of the brake pedal and the rpms jumped, and felt very similar to what happens on its own at random times. I couldn't get it to happen every time, but most of the time on light throttle at freeway speeds I could make the rpms jump up. I wonder if there is a short in the brake switch, or its not properly adjusted.

 

Make sure the WHITE switch is adjusted properly.

 

Not to distract, but sometimes people don't check the gap on new plugs. (it gets a little bigger each mile). It's never a bad idea to verify that they are at .o35.