Been a long time lurker, but could not find an answer to my problem so I created an account.

1999 Acura RL with 230k miles.

When the engine is at normal operating temperature I only get hot air from the heater when I am at mid to high rpms. The higher the rpm the hotter the air. At idle it blows cold. The fan blows strong all the time.

Thoughts? Thanks in advance.

 

sounds like you have an air bubble in your heater core. At idle there isn't enough fluid circulating in there to heat, but when you step on the gas it gets the hot coolant in there, heating up the air.

One test for this is to turn off the radio and turn the heat down to low so it's quiet in the car, and drive away from a stop sign or red light. if you can hear a sloshing sound, that's the fluid rushing into your heater core.

To fix this just fill the coolant and bleed the air out. But if the problem comes back you might have a fluid leak somewhere in there.

 

Exactly what he said.

 

ditto