[pater]

pawn Код:

NOS = SetTimerEx("NOSGiver", 1000, 1, "i", playerid);

You had vehicleid for timerex, which had to be playerid

also change NOS into NOS[MAX_PLAYERS]
than use

pawn Код:

NOS[playerid] = SetTimerEx("NOSGiver", 1000, 1, "i", playerid);
// and
KillTimer(NOS[playerid]);

otherwise you will disable the timer for all players when one player exits the vehicle..

good luck.