9 FJ-80, Heater doesnt blow hot air on idle (1 Viewer)

[Illfixit]

NEW PROBLEM. I noticed today while I was working on my sons FJ that while I sit and Idle the heater doesn't blow hot air.
When I press the gas it will...??? This is anytime, even after its warmed up and the temp is hot!! Took a drive and waited in a parking lot idling and back to cold. Anyone had this issue? Also noticed that lights and most everything does dim and slow on idle???

 

[Tools R Us]

What year? If it's a 3fe, the upper thermostat gasket maybe missing, allowing coolant to bypass, causing inconsistent flow.

 

[mct75]

Mine is similar, apparently the heater cores are known to clog up in these.

 

[pengfinn]

Mine does the opposite, idle is about the only time it's truly hot, usually just lukewarm.

 

[loquito]

back flush your heater core, To check hold on to both coolant hoses one at a time, if you find one hose is hotter than the other than your heater core can not pass enough fluid fast enough before it can cool. If the hoses are a different temp the hot hose is your intake, flush from the output side.

 

[Illfixit]

Ok , we'll try that, Thanks. And oh by the way its a 92, I see my s*** junk computer didn't like the 2 !!

 

[890man]

Check your coolant level. Mine was low and did this. The culprit is a small leak on the shaft of the temp control valve at the firewall. Mine is a 94 though. It never left a puddle under the truck so I missed it.