Hot Air Intake Valve not receiving vacuum when hot

[thetoyotaman]

I took my 40 for a good warmup highway drive at 60mph and discovered that the hot air intake valve is not receiving vacuum on the air cleaner. It appears that the hot idle compensation valve is not working. It there anything I can do to fix it or do I just need a new one?

 

[ColonelMustardFJ40]

I have a 1976 FJ40. The hot air intake on the air cleaner snout is not vacuum controlled. It is thermostatic and opens when the air being drawn in from around the header is of high enough temp. Not sure about your 82.

 

[subzali]

No, the HAI is open at cold temperatures to draw warmer air from the exhaust manifold area. Somewhere around 80-85 deg F it closes to draw air through the front of the air intake. On my FJ40, it's hard to discern the vacuum being pulled by the engine when I put my hand over the air intake.

 

[thetoyotaman]

When the motor is fully warmed up after highway driving it is drawing hot air in from the manifold, not cold air from the snorkel. Thanks.

 

[thetoyotaman]

I think I'm getting closer to the problem. My motor runs low vacuum and I think that is the underlying cause.

 

[studawg]

Is the HAIV related to the HIC? I didnt think they were related.

 

[studawg]

Well I figured out that on my 78, the HAIV is not related to the HIC, but on other models it is. I am still trying to learn more about the Hot Idle Compensation though, as mine doesnt want to idle when its hot!

 

[studawg]

When the motor is fully warmed up after highway driving it is drawing hot air in from the manifold, not cold air from the snorkel. Thanks.

This is incorrect, by the way. The system that you are referring to measures the temperature of the air coming in the air cleaner, and if it is below a certain point the HIC valve opens and it controls the diaphram that moves the HAIV to allow warm air from the engine bay into the air cleaner as opposed to outside air from the snorkel. It doesnt have anything to do with the temperature of the motor.

 

[Spike Strip]

HAI valve, under the air cleaner, is NLA.... I just plugged the hose to the flapper so it's down all the time.

 

[Fast Eddy]

This is incorrect, by the way. The system that you are referring to measures the temperature of the air coming in the air cleaner, and if it is below a certain point the HIC valve opens and it controls the diaphram that moves the HAIV to allow warm air from the engine bay into the air cleaner as opposed to outside air from the snorkel. It doesnt have anything to do with the temperature of the motor.

On a '78 the HIC is the Hot Idle Compensator and has nothing to do with the air cleaner valve. The air cleaner valve is purely mechanical with no vacuum control. On later models they may be tied together.

The HIC is the little box with the nipples. I think only one, on the right, is affected by the temp.

My '76 has a later model air cleaner with the HAIV. I'm not sure what it's connected to now that I'm thinking about it, but I know it opens, but maybe not depending on the intake air temp though.

 

[Spike Strip]

It's an '82 so it's going to be just like an FJ60. The HIC valve is NLA. So if you just put a BB into the tube to the HAI, it will delay warm up a bit, but you'll get cooler air when running, instead of heated intake from the exh manifold.

I went through 3 used valves and finally gave up. And it still looks smog-legal, if you have to do that.

 

[thetoyotaman]

So, does the HIC work better without a snorkel then from you all are saying? Im guessing the snorkel draws cooler air in?

 

[Spike Strip]

The HIC is supposed to operate based on incoming air temp, i.e., temps inside the air cleaner. Once the ambient air reaches a certain temp, the HIC bleeds air into the air cleaner, lowering the vacuum to the HAI diaphragm, causing the flap to lower, or close-off the pull from the heated exh, and then allowing air to be drawn through the snout of the air cleaner. Have no idea what a snorkel does to that, if anything.

I went through all this because I too could not get that flap to close (allow in cool air), even on 100* days here in so Cal, so that's why I disabled it. But I'm in so cal so it's really not an issue for me.