Heater only works above idle, At idle it's cold.

[Jeeves]

First off, it's a 1994 Camry XLE w/the 1MZ-FE. (Though I doubt that matters) I don't recall this as an issue in the past, and it seems mighty weird, but if I'm sitting at a stoplight or something, just at idle, I'll get cold air out of the vents regardless of how high I've got the temp knob. However, if I rev it to say, 2300 and wait, slowly I get hot air again. Is there a Heater VSV that could be failing or is this some kind of common issue? I tried searching but even just the word "heater" only gave me 3 results. It's startin' to get cold round NM so this problem has become much more appearant. Thanks for any help!
-James

[karazy]

This is a strange one, but I'm sure it can be figured out.
Need more info.
No mention of temp problem, so I'm assuming coolant level, thermostat and pump are ok.
Is the cold air change slow, like warm air change, or instant?
Is it the same with fan at low or high?
Does the temp control feel too loose or tight?
Does it get as hot as usual, when it is warm?

[amerikim]

Jeeves, not trying to yank you, do a search on vents.
I do remember something about the XLE's electronic controls misbehaving,but don't have the details. Vent was letting cold air in. It's here and been discussed.
But how is your car's running temperature? Does the car's temp gauge indicate steady? Reason I ask is if your thermostat is possibly stuck open, allowing your car to cool back down. Hence the cold air.
Another way is possibly your cabin heat exchanger is blocked, not allowing flow in low pressure situations. That is located under dash, passenger's side.
Get warm.

[Jeeves]

There's no temp problem to speak of, it comes up to temp (a little shit of the half way mark) and stays there. Always, never EVER seen it raise or dip. I've had to refill the coolant a time or two, but there's no coolant on the ground, and I don't have a blown head gasket, and I don't feel coolant in the passenger floor, so I'm not sure where it cold be going. However, like you said, since I see no temp fluctuations, I assume all those are ok.

The change from hot to cold is like you'd expect if you started up your car cold, and then drove down the road at 90mph, except it heats up faster. 15-20seconds on the gas pedal and I'm back in the heat again, if I let it idle that long, it's back in the cool.

cabin heat exchanger

Is this the same as the heater core?

Fan speed doesn't seem to affect it at all.

The temp knob seems sort of sloppy, like if I throw it all the way to the hot w/o hitting the extreme it doesn't get there. It's tough to explain, but if I want hot, I turn it all the way to the hottest, then back off. If I want cool, I turn it all the way cold then change from there.

When it's warm, it's warm, but it's not quite blistering or anything.

Thanks again guys, I know Supras, not these Camrys

[Pineapple]

Not enough coolant flow at idle? Plugged heater core? Bad coolant pump? Ever try a coolant flush? Coolant switch stuck and can't open all the way? Somehow AC was turn on?

[karazy]

Although there is something wrong with the mixer ( heater control), usually the fan will overcome this on high. I'm thinking Pineapple hit it , in his shotgun spread, with the partially clogged heater core. The pump increases pressure when the RPMs are higher and that provides the heat when driving. A really good flush may fix it. Make sure the heater is on hot. You'll probably be better off to connect directly to the heater hose.

Flushing is way easier than changing the core.

[Jeeves]

Originally Posted by karazy

Although there is something wrong with the mixer ( heater control), usually the fan will overcome this on high. I'm thinking Pineapple hit it , in his shotgun spread, with the partially clogged heater core. The pump increases pressure when the RPMs are higher and that provides the heat when driving. A really good flush may fix it. Make sure the heater is on hot. You'll probably be better off to connect directly to the heater hose.

Flushing is way easier than changing the core.

Trust me, I understand that. I've pulled 5 7MGTE Motors out of supras and I'd MUCH rather do that than deal with replacing the heater core (I've had to do it once in the Supra). It took 6hrs IIRC.

On High, the fan just blows out cold air. Just in much greater quantities. Is there any chemicals I can flush the core w/that would eat out gunk caused by coolant buildup/dryout? or just lots and lots of water?

[karazy]

On High, the fan just blows out cold air. Just in much greater quantities.

Can you get any heat, at any time, when the fan is on high? If not, I would check the heat mixer controls first.

Yes, there are rad flush products. I don't know anything about their effectiveness, though. For a couple of bucks, I guess it couldn't hurt.

[dna59]

I'm the complete opposite of you. At high rpms my a/c works and at low rpms it doesn't. Sometimes even at high rpms it doesn't work(light blinks) unless I have it on high. Any one know what that prob could be?

[Jeeves]

I don't know what the light blinking light means.

If I'm at a > idle RPMs, I can get the High fan speed to push HOT air just fine. It's just the at Idle that gives me issues.

I.E.:
I start up the car cold, and drive it with the heater selector all the way to hot, and the fan speed off. Then once it reaches operating temp (needle just shy of the middle of the temp gauge) I turn the fan on (to any speed) it will work as long as I'm not at idle or close to it. If I'm just at a stop light idleing (sp?) the air coming out of the vents will be cooler air, not hot at all. If I then shift into Neutral (Automatic) and hold the gas at 3,000rpms the air will warm up and be just fine. If I let off again and it comes back to idle(ish) speeds it'll be cooler air again.

[Nico]

Very strange indeed. The first thing I would think of when it comes to heating is replacing the thermostat, it is a cheap part, and it is also damn easy to remove on these engines. Anyway it is not a bad idea to replace it from time to time. Apart from a flush of the entire system I don't see any other link between these two elements : engine at idle and no heating. I dont see how it could be an electric problem whatsoever.

[backotruck]

Cheap fix....I bet its a plugged heater core as a result of Red coolant mixed with green. When the F'n dealer drains any coolant, they replace it with red fluid. The red is a longer life, which Toyota has since told their dealers to quit saying. If mixed with green, it will gel. Clogging your system. Get it flushed immediatley and stick to the green kind. Find the strongest cleaner you can find. If you flush yourself, don't over flush as a garden hose has a psi of 55-70 and a coolant system is 22 psi. Good luck!

[burchard]

Looks like a low coolant flow, probably due to an execss of deposits in the core and/or the valve is not opening all the way.

[jhbhatia]

i think all are right. Its really hard to tell you what to do, since a lot of us are puzzled as well. Easist way to try to cure this is to replace the thermostat and flush the coolant. THey have this prestone flush thingie, helps flush radiators...i tried it, didn't really help..but you really need to flush a lot after that. I'd suggest you run on water for a day just for that to be totally out of the system. i tried it for 3 and still has that thing not coming out clear!!!

[mobes]

Mine is doing this now too