My gals 93 YJ runs like a top when cold and first started. It will run great for hours until I shut it off and try to restart it. Some times (not all of the time) we are experiencing a bucking/jerking worse than a cowboy riding a mad bull, It almost feels like the thing jumps time. Its a 4.0 with fuel injection 5 speed. After the jeep sets and cools for a while she starts and runs again without a problem. The O2 sensor and fuel filter have been replaced a few months ago. Could it be the crankshaft sensor? Thanks in advance for any help/comments. Frank