1999 saturn sl2 sometime will start sometimes wont, engine wont even turn over after driving and then park has to sit and keep trying to get engine to turn over any suggestions

Check coolant temp sensor.

sounds like you need to replace the temp sensor

Sometimes the security-anti theft systems go bad in these cars. Actually in ALOT of GM cars. This will cause the car to either "not start" (as in the starter wont even turn over) or start for 1-5 seconds and shut off. You might also notice a light somewhere on the dash that says security when this happens. If this sounds like your problem, check out this link for info and some DO IT YOURSELF solutions. http://vatspasslockpasskeysecurityhelp.yolasite.com/

SOUND LIKE ALTERNATOR NOT CHARGING BATTERY.CHECK BATTERY VOLTAGE SHOULD BE 12.6 VOLTS.MAY SURE BATTERY CABLES CLEAN AND TIGHT.WITH ENGINE RUNNING CHECK ALTERNATOR OUT PUT AT BATTERY.SHOULD BE 13.5 - 14.5 VOLTS WITH ENGINE RUNNING.IF ALTERNATOR FUSE GOOD AND ALTERNATOR BATTERY FEED WIRE AND VOLTAGE REGULATOR WIRES OKAY NOT DAMAGED.DRIVE BELT NOT SLIPPING OR BELT TENSIONER NOT DAMAGED.ALTERNATOR MORE LIKELY FAULTY.TURN OFF RADIO FIRST.BEFORE REMOVING NEGATIVE BATTERY CABLE TO KEEP FROM LOSING RADIO CODE.

check the alternator and the battery...

Sounds exactly like my 1999 SL2 which had "burning and arching" in the fuse box. Car one day be fine the next I'd take it to the store, come back in 10 minutes and wouldn't start, no radio, no power windows, no keyless entry remote, no rear defrost and even locking doors from inside power buttons it sounded odd. This fixed the problem by replacing the fuse box.

Guessing there may be two issues. One might be "burning and arching" of the fuse box. My 1999 SL2 would periodically not even make a noise to turn over and that fixed that. It also had issues that some electrical components wouldn't work at the same time.

yes, remove starter taka it to a service shop for servicing and checks , also check the condition of the battery,make shore it's holding charge and cells are ok.

check timing belt!! good luck!!

You might want to start by checking the wires to the starter. I've seen those little buggers age and develop cracks in the insulation causing intermittent starting issues especially if the battery is good and it feelslike it's cranking slow. You might also want to check your alternator to make sure everything's charging properly. If memory serves there was a tsb for these cars regarding the charging system and I think even a recall for the rectifiers.

WIthout trying to turn it over, turn the key to the on position and listen. You should hear your fuel pump prime. If not could be a bad fuel pump relay or maybe a bad wire to the pump, or even the pump itself.

Do you remember the specific codes you pulled from the computer? Especially the ones from when it stalled after replacing the computer. Those might also be helpful in putting you in the right direction on this.