03 heater cools during idle

[03AZExploder]

I've checked coolant level which seems to be fine, and my temperature gauge doesn't fluctuate at all. Is this more likely a heater core issue, or a water pump issue?

 

[Hudsonf]

Sounds like the cooling system may have a air pocket and needs bleeding.

 

[rocco123]

Make sure u have vacuum at idle. If u do t have enough the valve will close at low rpm