• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Rough Idle/Losing Power


NAXJA Forum User

96 Cherokee Sport

Background, cat had been blocked for a little bit. The car started to lose power under load and would occasionally start to choke out while idling at a stoplight or traffic etc. So I dropped the cat and ran it without exhaust for a few days while waiting for the new system. Car ran extremely poorly, but randomly. I could drive for 10-15 miles then it seemed like a cylinder was misfiring and the car would shudder and lose power. Seemed especially prone at high speeds, but pulling over/turning the car off seems to occasionally fix it.

Since then I have added exhaust system, still no cat (backordered), and replaced spark plugs and wire. Old spark plugs had a reddish orange color to them like the car was running lean and a little carbon fouling, but nothing egregious. That seemed strange since I thought a clogged cat would make the car run rich. It seemed great for a few days, but just now I was letting the car idle and after 3-5 mins it started to run really rough and almost dying. Car was parked in a sloped driveway, and car seems to have most issues when going up an incline. I am thinking maybe I need way hotter spark plugs? Other idea is the O2 sensor is not reading anything other than open air, but I have searched and that doesn't seem to be a major issue.

Went from Champion RC12LYC to NGK FR5-1 7252 for the spark plugs.

Any help is appreciated.
Sounds kind of like what mine was doing. it got progressively worse until finally, it would often completely crap out *after switching from open to closed loop* after a few minutes of driving on a cold motor. Turned out to be my front O2 sensor. It never threw a CEL code until after it completely dyed, no code while it was acting up and slowly dying. While the O2 sensor was slowly failing it would occasionally just crap out, usually at slow speed or idle, but sometimes it just ran bad, missed and bucked randomly.
O2 sensors and fuel pressure are likely suspects. If the NGK are the recommended substitute for the RC12LYC they will be fine.