Blend door issue?

[Indytona675]

Ok. 1999 XLT 4.6l black (because color is the most important)
Heat is nice and hot...as long as I'm driving. When at idle, stop light etc, the heat fades all the way to cool/cold depending on how long the light is. Once I accelerate the heat comes back. Im guessing this has a vacuum blend door issue. How far apart do I have to take the dash to check it and what would be the best way to check?

 

[designit]

All the way out I'd think... (that's the bad news) -- But the good news could be that it really doesn't sound like a blend door issue (imo)... Maybe a thermostat ?

I just had my dash pulled for a heater core / blend door actuator (motor) replacement & to me, it would seem quite odd for the blend door to open and close based on idle. - The actuator (wire connected to the dash dial) opens and closes the door.

my 2c anyway.. good luck

 

[jrjr]

Sounds more to me like a compromised water pump or partially clogged system.

 

[walnuts4x4]

just a thought... back when I was in the Air Force our impala patrol cars would act like that when the coolant got low... have you checked that?? just my .02

 

[driveway2fast]

Most likely NOT the blend door (that is controlled electronically)
Climate control system uses vacuum to direct the air flow (vent, floor, defrost etc..) so A vacuum leak would be different symptoms

As mentioned above I would check your coolant level first, then water flow/thermostat

 

[CARO'S98EB]

I agree.i would look to flush the heater core, but is most likely the water pump vanes are worn away, reducing the flow at idle.

 

[Indytona675]

Why do I over think stuff. Coolent was low. Ill keep an eye on it to see if it goes down and I have a leak but everything looks dry. Blend doors haven't been vacuum for quiet a while. I feel sheepish. But hey ill admit when im way off. Thanks all for the very polite did you check the coolent first suggestions.

 

[Indytona675]

Well goody. Coolent level is fine. Now im getting very little heat. Then I remembered oh-yeah this has rear heat as well. Rear heat works just fine. Nice and toasty. Looks like it is blend door related. I think I saw a you tube how to check video. I loath pulling the dash. Not difficult usually but time consuming and very annoying. At least its not ebbing related.