I just picked up a 2002 Grand Cherokee wit the 4.0 liter. It was idling okay with just a little hiccup. I changed the spark plugs and now it is idling the same but every now and then it sputters and then the engine dies. I was hoping someone had any ideas about what to try next.

 

have you cleaned out the throttle body? sometimes carbon builds up in there and causes erratic idle. completely remove it (its easy) and clean out all passages and make sure the electrical connections are good.

 

Clean the IAC valve along with the throttle body.