Rb20/25 Air Regulator Purpose

[kumasan616]

I have read/heard several responses to this device.

The Air Regulator, which on an RB20 sits in line with the fuel rail, is connected with a tube leading to the bottom of the throttle body, and another leading to a "T" that connects the AAC back to the intake tube just before the throttle body.

What purpose does this device serve? Can I eliminate it?

[gawdzilla]

it is a restrictor that fully closes after the car warms up completely. it works with the AAC to bump the idle up when the motor is cold starting. i don't know what would happen if you got rid of it. if you just bypass it completely you might have a high idle all the time. if you block it off your car might struggle with cold starts and take longer to warm up. why not just leave it in?

[Carl H]

bumps cold start up to around 1-1.2krpm idle...bimetalic strip inside is heated until it closes all the way heating is done against water temp.

[kumasan616]

If it is stuck open could it cause an engine to run lean? If bypassed (i.e., plumbing from the T to the bottom of the throttle body), outside of not having a higher idle during cold starts, what other impact would it have?

[jdmser]

Don't do it. I've tried it on a SR20 and it ran like poop at idle.

[kumasan616]

I am trying to isolate a problem associated with the following conditions:

cold start: idle hunts from high idle to barely running, all 6 cylinders firing, smells rich.During warming: runs a little rough at idle, 1K-1.2K idle. hesitates intermittently, all 6 cylinders firing, pulls decently, idles smooth 3-4 min after initial startup.After about 7 min (my guess): idle goes from smooth to what sounds/feels like a slight misfire/sounds like a subaru. Smells learn. Performed O2 sensor test with mode 2 in the ECU: light 90% stays on at 2K rpms, no load.

...and I didn't want a Subaru. So I am trying to fix it.

I am theorizing that it may be a bad air regulator that could be causing my problems for several reasons:

1. FSM says air regulator closes fully after 7 min. My problem gets goofy after the same amount of time. 2. 2-plug connector is broken and held into plave via zip ties.

Modified by kumasan616 at 11:02 PM 1/20/2009
Modified by kumasan616 at 11:09 PM 1/20/2009

[240z4u]

The sensor is "dumb" for lack of a better term, its not really even a sensor. I don't have mine installed at all but I plan on putting it back on at some point. It it likely not causing your issue.

Sounds like coolant temperature sensor or your idle air control taking a poop.

Evan

[kumasan616]

hmmm... interesting. Well temp sensor is new, and after installing it, no change. AAC valve has been cleaned, is within specs (ohm test), good continuity at harness connector. Not sure what else to do if the air regulator isn't causing my problems.

Also, what US spec equivalent replacement matches the RB20DET air regulator, in case I need to replace this one (if it is faulty)?

[240z4u]

Warm the car up, unplug the bypass and clamp off one side of the tube with vice grips. If it still idles weird that isn't your issue.

Evan

[kumasan616]

okay thanks I'll give it a shot. That I believe will be a good test for the idling issues, however not my off-idle lean condition. If the air regulator is not closing properly (allowing air to escape through the bypass), then even though the ECU senses the signal is closed and shuts off the extra fuel for the cold start, runs lean because the cylinders are receiving extra air (above sensed value at the MAF) past the air regulator causing it to run lean? It would seem that a sensor is causing incorrect readings to me...I am pretty certain there are no air leaks anywhere, and I am sure the fuel system is in good order (freshly recalibrated injectors, new fuel filter, pressure tested fuel pump and flows fine)

[240z4u]

I need you to read this very carefully.

That is not a sensor, and it provides no feedback to the ECU at all. All it is is a bimetallic strip that has power applied to it and gradually moves. Its not controlled by the ECU its not even a sensor. All it has is power/ground.

This is not to say that it isn't leaking and causing your idle issues though.

Your TPS is where I would start.

Evan

[kumasan616]

Understood and thanks. I should have included the ECU using the signal from the Water Temp Sensor to adjust for extra fuel during warm up in my post above.

For my understanding, the signal from the water temp sensor going to the ECU allows for power to be sent to the "device" (Air regulator), heating the bimetallic element, causing it to close. During warmup conditions, this device would allow for extra air to bypass the AAC valve during warmup, causing high idle. When it closes, the air flows only through the AAC valve, lowering the idle.

I'm going to inspect the device anyway for leaks and proper function. If it is not working properly, it should logically cause some issues, and will be replaced. I will check the TPS as well, I have not tested it yet and didnt think of it because the idle only stumbles briefly, then is fairly constant otherwise.
Modified by kumasan616 at 12:24 AM 1/22/2009

[240z4u]

Quit messing with the air regulator for a minute and check your TPS voltage. I am willing to bet thats the real issue. I wanna say .46v @ idle is the trick.

If your regulator is stuck partially open it will idle high.

Evan