update on my 97 88ls dying on me for no reason....

as you'll know im a newbie...im in the air force and am gone alot so i need to get my wifes car fixed :)..this is my wifes car i originally posted my ad about the car either being at a redlight,stopsign,driving and the car JUST DYING...i dont mean hesitating then dying like from fuel...but like someone turned off the ignition switch!...we tried diagnosing it,then took it to the dealer who had it 5 days and said they "couldnt get it to duplicate" famous words,eh? some of the guys here said its with the crank sensor, or the icm.......now heres the funny part...someone here at home told me to replace my 195 thermostat with a 180 they had the same problem with a gm car.....i did it and while i had the radiator cap opened i saw on ungodly sight of rust and crap in her cooling system! i replaced the thermostat and the car didnt die for 2 days...it was cooler outside...on the day i gave it back to my wife...it was warmer outside and the car just dies again......whats up? i know i really need to drain my system and clean it oout and put new antifreeze in.....put does anyone have aclue about why my car is dying?....im trying not to spend 500 bucks to find out that didnt fix the car.....but wierd about the car not dying when it runs cooler....

It has to be scanned when it dies I assume it doesn't start right back up, no info here. When scanned look for an rpm reading when cranking if none, usually the crank sensor or bad connections to it, 2cn possibilty is the icm, but some of this can be guess work without on site diagnosis.