Problem restarting 1992 Jeep Cherokee

[Cilly]

My Jeep needed a starter 7/06. Money tight...bought from junkyard. Lasted 3 days, bought a new one and replaced negative cable per Mfg. recommendations. I have a 6 cyl. 4.0 2wd with 214K plus miles. The engine light came on about 3 weeks ago and since that time, the idle has seemed higher. Now I have the situation where it starts right up and dies right away. When I start it up again, it's okay and will get me to work (about 30 min.). If I try to start it again after being driven, it will not start. When I turn the key to the first click, I can hear the fuel pump give that little hum that it is working, but when I turn in to the starting position...nothing. If I leave it alone for several hours, it will start up just fine. I have taken it to a mechanic several times, but it never misbehaves for him...only me. Can anyone advise me on this? I have been dealing with this problem for 3 weeks.