What is causing my 98 Cherokee inline6 4.0 to stumble or skip under load? In P or N idle is nice and smooth. Drop it into R or D and it idles low stumbling almost like it isn't getting gas. Fuel pump is operative. Cleaned intake and TB. Tossed platinums and replaced with new copper plugs. Wires, cap and button fairly new. I have tried fuel treatment. Once I get on the road I have no issues, drives great. The dreaded stop sign or red light isn't so great. Hasn't cut off on me, but has threatened to once. I am no mechanic, but choose to do repairs myself in order to better understand engines. Not sure how to check for vac leaks. Not sure I need to. Any help appreciated, thanks forum.

 

When was the last time the plugs, dist cap, rotor, and wires replaced?

 

Plugs, wires, button and cap are new inside of 6 months. Upon replacement I had issues with skipping, and traced it back to faulty cap. Had to replace cap twice before finding a good one. Have not had an issue since other than a fouled platinum plug here or there. So this week replaced plugs with copper. My current stumble issue doesn't seem to have the same symptoms of when I had a faulty cap. such a cheap, plastic design. I have two jeeps with similar engines allowing me to trade out parts, handy when it comes to troubleshooting.

 

Seems to worsen in warmer weather, or when engine is nice and hot. only under load at idle.

 

MAP sensor, Coolant Temp Sensor (the one by the thermostat can cause hard starting and mixture issues), IAC valve. I would check those things.

 

Torque converter?

Max