The heat in my 2003 mit mont sport only works when you are on the gas. And when you are at at stop light cold air lows out.

How to Fix Car with No Heat Easy YouTube

the heater cre needs replacing replace it and enjoy heat again

I think you could use this manual method instead.. My nephew used it
to repair my car and it's totally perfectly fine now. Here's the website he bought it from. www.reliable-store.com

ask a local mechanic to have a look at the causes could be numerous from a fuse to low gas and lots os sensors inbetween

My 2003 Monte Carlo and my husbands 2003 chevy pickup both had the ABS and traction control lights on. When it began it only came on once in a while but got worse until the lights were on all the time. After several attempts to find the problem we purchased a ABS Brack Scan. Part #CP9449. Although it doesn't pinpoint the exact problem it does tell you what wheel has the issue and possible problems. My problem was a bad wire in the harness. Good luck!

Re the a/c. Get a can of red tek sealer. make sure the engine is cold or you won't get the connector on to the low side port to seal properly. Follow the insrtuctions that comes with the can. Just adding the refrigerant doesn't stop the leak

Sounds like you are low on antifreeze.Or you have air trapped in the coolant system.

I had same issue. Turns out it was low on anti-freeze in the radiator. I added fluid and now have lots of heat!! Be sure to also add radiator fluid to the overflow tank too.

try changing the thermostat

Take off the radiator cap when the engine is cool, if the radiator is low replace the cap and fill the rad up to the top.