1997 Mazda 626 starting problems

Other Category problem
1997 Mazda 626 4 cyl Wheel Drive Type unknown Automatic 167000 miles

i brought this mazda 626,now i understand that with167,000 miles on the car im going to have problems,but im trying to find out what may be the practicular problem with this situation.okay i drive the car only to work and back home but lately about every so often i may go to the store and come back out and the car won't start so then i leave the car there all night and go see if it'll start and it starts then about 3weeks later i have the same situation.i know the car hasn't had a tune up in maybe over a year,do know what maybe the cause of this i had the car checked several times by a mechanic and as far as the battery,alternator,and starter everythings fine so what do u suggest?