Idle-up diaphragm - Toyota Nation Forum : Toyota Car and Truck Forums
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#1 Old 04-01-2011, 03:20 PM
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Idle-up diaphragm

Got a question about the idle-up diaphragm on the Aisan carburetor.

What exactly is the purpose of this thing? I have had my truck for 6 or 7 years and it has never been connected to a vacuum port. With the adjustment screw down as far as it will go and vacuum applied, it idles the engine up to around 3000rpm, though it's possible that the original adjustment screw has been replaced with one that's too short.

Repair manuals are pretty vague about it and I can't see in the vacuum diagrams where it is supposed to be plugged in.

The fast idle cam does the job of kicking the carb to the proper fast-idle speed, so it seems that the "idle up diaphragm" is either redundant or just completely useless.

As always, everyone's replies are appreciated.

1985 Xcab/22R/5Spd MT/2WD/152,000mi - All stock daily driver
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#2 Old 06-25-2011, 02:40 PM
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I have an 85, 22r, 4 speed, 2.4, and am the original owner. I too dont know exactly what the idle up diaphram does, but, I dont think mine is working and it might have something to do with kicking up RPMs for your ac compressor.

I have tried to adjust the fast idle but cant get the rpms to go up at all. Mine did not come with ac and about 5 years ago, put one on. When the truck is stopped in traffic, I have to goose the gas to increase rpms and keep the ac cooling. Might not be related to the idle up diaphram, but, the engine never kicks up rpms when the compressor kicks on.

Take care. will post info if I find something new.
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