My 1996 Olds LSS doesn't idle properly,idling surges sometimes,the temp. gauge doesn't work and sometimes the heater doesn't work.It may stall while driving.If I get in and the power seats won't work or the power windows won't work I know the car will turn over but not start.We have replaced the main computer,the idle control sensor,the crankshaft position sensor,checked all the fuses.Presently there is no fire to the fuel pump[which is also new] and no power to the windows or power seats and will not start.

Heater core is not working.

Check temp gauge if It doesn't get to normal heat range it won't idle. Your thermostat needs replacing.

The temp gauge will go up due to the added load of the AC on the cooling system, and as long as it doesn't overheat you are fine. I would have the system checked for a low charge, the symptom,s fit. You will need gauges and then the pressures tested to find out what the system charge is doing.

For car running hot and overheating issues, I suggest to you go through this help links. Click this link below and go through the troubleshooting procedure to take care of the problems: ----Car runs hot? http://howtobyme.blogspot.com/2011/11/car-runs-hot-in-traffic.html
-----------All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html
Car freeze overnight and started overheating while driving?http://technoanswers.blogspot.com/2012/01/car-freeze-overnight-and-started.html-----------Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

---------------------------
Car overheats and Air blows hot at idle?
http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html
--------overheating? http://schematicsdiagram.blogspot.com/2011/12/buick-century-overheating.html
----------Car engine Overheats and transmission starts slipping?http://schematicsdiagram.blogspot.com/2011/12/car-engine-overheats-and-transmission.html
----------This details will help.Thanks.

Try to get a used instrument cluster. At any junk yard...

As long as you are not going into the red section you are fine. Most GM cars normal operating temperature is between 190 and 220 or so. Depends which engine you have.

What degree thermostat did you have put in it they make all different degree thermostats.

Timing belt/chain may have been put it slightly off time, when motor rebuild

you must have your car put on a diagnosis computer

you either have a intake leak or head gasket. get a pressure test and then youll find the leak......like i did. $800 later. and start looking for another car......