marase415

Just bought a 1998 Cherokee classic, can't figure out what's wrong with it..
If it hasn't been started in more than a few hours, the intial start up is rough. Cranks for 3-5 seconds before it actually starts. But after that, it starts right up- no problem. Also, if you let it sit and idle, after 5-10 minutes it will randomly start idling real rough & then starts misfiring pretty bad. Then after a couple minutes it's stops and starts idling perfectly normal again.. can't figure out why. Stops misfiring and sounds fine if you rev it up while it's doing it. It doesn't have a sticker so it's not driven- not sure what it's like when you're driving & it happens. I've considered it being a bad O2 sensor or crack in the exhaust manifold since it does need some exhaust work, but I'm not sure. The motor is mint so I doubt it has anything to do with the engine itself. Guy I bought it from said he replaced the throttle position sensor multiple times to fix the problem but it always came back. Any other possibilities? Has this ever happened with anyone else?

Jeepin'_Aint_EZ

Are there any codes? Could be the upstream o2 sensor on its way out, could be the fuel pump or could be a combination of the two. Ive had the starting problem. Was the fuel pump before it bought the farm. I've had the random rough running. That was the upstream o2. Testing needs to be done before being able to truly narrow it down

marase415

Yeah it throws up 2 codes, one is for an O2 sensor and the other is for an exhaust leak- so you're probably right haha

Thanks!

Jeepin'_Aint_EZ

It's a good starting point but the o2 code may be caused by the exhaust leak. Fix the exhaust leak first. Most likely a cracked manifold.

For your initial start-ups after sitting a while, do, what we call around here, the poor man's prime. Turn the key on (dont start) for a few seconds, then back off, then back on for a few seconds and then try starting it. Should fire right up without stumbling. This just indicates the drainback valve in the fuel pump assembly is bad. Pretty common. You can continue to poor man prime it until it needs a new pump but just make sure you put the whole assembly in so it fixes this problem.