Heater Problem
 

I have a 1997 toyota camry. I am having a problem with my heater it does not blow hot air unless i am accelerating then when i let off the throttle it cools right back down. I just replaced the thermostat and it didnt change the problem i can not figure it out? any suggestions?

Could be a few issues:

The heater control valve is not fully open, stuck. This is located in the engine compartment.

The heater core is partially plugged up. If this is the case try flushing the core out with a garden hose via the heater hoses in the engine compartment.

Sometimes the heater duct doors under the dash fail to move properly allowing not enough hot air or too much cold air.

Check the valve, then the core for plugging.