I have a 2003 LS that all of a sudden shut off on me yesterday while driving. When I say shut off, the engine just died. I tried restarting it and it would turn over and then shut off. I got it towed back to the house and replaced the fuel pump because I was having issues with the sending unit and thought that would do the trick. I turned the car on and it started up without any hesitation and ran in park for about 10 minutes. As soon as I backed out of the driveway and pulled down the street, the engine shut off again. It still shuts off when I turn it over like yesterday. Another thing I noticed, is the RPM gauge is jumping all over the place when the motor trys to stay on.

Anyone have any ideas what might be causing this?

 

Probably a sensor problem. Commonly, the MAF does stuff like that without throwing a check engine light. However, it could be the crankshaft position sensor, cam sensor, ignition module...

 

Luckily it was just a tune up. I replaced the spark plugs and wires and it runs like a champ now. Thanks for the input!