Heater Troubles The heater only blows hot air when the car is moving, when it's not moving it blows cold air. Is it the heater core or something else.

What have you checked so far ?
Radiator full of coolant ? Heater hoses getting hot ?

What kind of setting do you have? is it turn knob, push button or something else?

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

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Engine Overheats and heater blowing cold?

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

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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This will help.Thanks.

Possibly the heater core is 90% blocked. open enough to draw hot water in, (hose feels hot) but not enough volume to provide heat from very cold air, 10% hot water gets cold quick, coming from core..
Flush heater core in reverse direction - cold side in hot side out..

Just a theory..

Your heater core could be plugged with dust if this problem came up slowly I would suspect that. Another thing that cold be wrong is a trap door is not opening these are operated by cables vacuum or stepper motors. Confirm that something happens when you move from cold to hot on the control.

The problem was a vacuum line leak. Replaced the line.

Yes clogged heater core may be the answer in your case .

my 2004 pontaic bonneville the heater hoses going into and out from the heater core are hot , but the heater blow cold air. ,

Does the car run cold or is the temp. correct. Check the thermostat first. check that the radiator and res. is full. Check the hoses to and from the heater core. If one is hot and one is cold then either the shut-off valve to the heater core is defective or the heater core is plugged.

The heater in your car depends upon a flow of hot coolant going through the heater core in order to get hot air into the car. If the heater core is partially plugged, it will restrict the flow. If you have a head gasket that is putting exhaust into the cooling system, it will eventually get into the heater core. When this happens there is no coolant in the heater core to make the air warm. If the water pump vanes have corroded away the result will be very poor coolant circulation causing the heater to not blow hot air. If your car is equipped with a heater control valve that is not functioning properly, the coolant flow will be restricted. One or a combination of these factors is likely the culprit in your case.
if the car is not overheating, the thermostat is working fine.... replace or flush the heater core multiple times to try and eliminate sediment build-up.