2000 pontiac sunfire wants to stall out at stop lights or when I am sitting still it is fine on the highway I have changed the fuel filter, the idle control censor the air temp. censor.

Could be a dirty throttle body or a faulty idle air control valve.
Is the check engine light on ?

have the check engine light checked at a parts store its usuall free. I would bet its the idle air control motor. This controls the fuel air mixture at idle

you mat want to check the throttle body and make sure the throttle plate is clean from tarnish build up. you may also want to check for vacuum leaks around the throttl area that can cause an unsteady idle. a faulty MAP sensor can also create an idling problem but run good at highway speeds.

Classic bad ground to the fuel pump...Mine did it untill I hard wired it to a switch with a power light. Car stalls light out I throw the switch and im in control but remember to shut it off or your battery will be dead lol.

Change the fuel filter and the spark plugs.

if it feels like your driving a standard transmission ,and "you came to a stop light without pushing clutch in"
that will be the torque convertor lock up,

i'm not being smart, but do you know for sure you are installing the thermostat correctly? the thermostat is there to slow the water flow down long enough for the water to obsorb the heat .also is the cooling fans operating ?do the fans come on at around 210 degrees?is the radiator grill clean? lower spoiler intact? does the engine over heat at highway speeds or while idling? are there any codes?is the engine running lean? possible fuel filter stopped up.fuel injectors dirty. let me know

the lock up converter is staying engaged when you stop have it scanned for trans codes may need lock up selinoid (tcc) or torque converter changed try putting it in neutral before you stop if it stays running this is probibally your problem

you may have a faulty ECM

try changing your fuel filter