2007 Chevy Impala blower?

Bleed the coolant sys, Poor heat at idle, however, if the engine RPMs are raised the concern no longer occurs. With the engine cooled off, remove the coolant pressure cap.
Remove upper heater core hose from the metal pipe on the engine.
Add coolant to the metal pipe, until full.
Raise the rubber portion of the heater core hose as high as it will go with it still attached at the heater core. Using a funnel, add coolant until the hose is full.
Reconnect the heater core hose.
Start engine, have assistant raise the RPMs to about 1500 to 1700 RPMs, top coolant off at engine, then before lowering engine RPMs, install the coolant pressure cap.
Fill coolant reservoir as necessary, then check the heat at idle.
Note: If there is still a lack of heat at idle, perform the cooling system draining and refilling procedure
follow this info, if it dosent work pressure test it for leaks.