Hard Start/Non-Idle

Went to start the '99 earlier this evening and...one brief fire but didn't start. Not uncommon...but, then no further life... After hooking up jumper cables to ensure good cranking rate, it wouldn't fire at all until I tried giving it gas pedal...after which it started, but wouldn't stay running when allowed to throttle down.

There was a fair bit of rain in the last 24 hours, and it hasn't been run for a few days, but that is very atypical. SOUND like a sensor gone south....?? [I haven't been back/able to check for any codes...]

Thanks for any informed input.

On newer Cherokees when you let the battery run down by leaving on the lights or it gets old enough that you loose one of the cells the low voltage will cause the engine computer to loose it idle settings. The symptoms are rough running and the engine wanting to stall if you don't keep you foot on the gas. After 5-10 minutes, the computer re-learns the idle settings and the engine will idle like normal at about 600-800 rpm's with no stalling.

Have the battery or alternator load tested if you think they should be retired.