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My 89 cherokee 4.0 has recently starting idling rough, I tried tuning it up and it does run better but it still idles a little rough. Along with that it kind of hard starting and in the haynes manula it says its due to a weak ignition,
anybody have any idea which part they may be refering to?
Also, my plugs were black from it obviously running to rich, okay fine but how do you adjust the throttle body?
Thanks,

 

How long has it been since it's been tuned up? What condition are the cap, rotor, wires, and plugs in? Check the coil.

 

Could be that your O2 sensor has failed. Unplug it and see if it runs better.
When O2 sensor fails it will normally set a rich condition. Unplugged the ecm sees a .5volt refference and adjusts fuel trim acordingly

 

you can pull the O2 sensor, heat the tip with a propane torch for a solid two minutes and then try it, you might unblock carbon from it that way and save a few buck