1999 pontiac montana no heat when sitting still

Hi i have been having trouble with my heat in my 1999 pontiac montana. When i am driving it works great but as soon as i have to stop at a light or whenever its just idle sometimes i get just cold air and sometimes i get very little air if any but as soon as i start to go the heat kicks right back up and works great i was just wondering if anyone could help me out with this problem thank you

That is a symptom of low coolant or air in the cooling system.

these vehicles will move less coolant at idle than at higher rpms which means less heat output at idle but it shouldn't go cold.

i had my mechanic bleed the system and also the coolant is full is there anything else it could be especially with it blowing cool air at idle

i had my mechanic bleed the system and also the coolant is full is there anything else it could be especially with it blowing cool air at idle
Sounds like you need to verify that water is flowing through your heater core properly. Maybe you should flush your heater core and check to make sure the hoses to it are clear and not kinked.

is it something that is difficult i know that some you have to take the whole dash apart to get to the heater core

is it something that is difficult i know that some you have to take the whole dash apart to get to the heater core
You should not have to open up the dash to see if water is flowing through the heater core. There are two radiator hoses that go into your firewall in the engine compartment. One is the in and the other is the out. These are the connections to your heater core. Disconnect them and see if you can force water through from your garden hose. Then reverse the direction. See if any crap comes out. Also make sure the hoses that are connecting to the firewall are not kinked or blocked.

your heater core is 10 years old so be very gentle removing the lines from the core otherwise you could break the heater core. Sometimes air can get trapped in the core and it can be difficult to bleed. opening the lines will let the the air out. backflushing while your in there is a good idea.

On some stubborn systems I had to open the heater outlet line with the engine running to purge out the air. Just make sure the coolant is cold.

did you check to see if the thermostat was good?

you might want to inspect your cabin air filter. if its plugged like mine was at idle little to no air passed through the vents. easy check, no cost.