what does the bypass control solenoid valve do?

[zedjr10]

I got a 92 accord with f22a6 engine with M/T. What does the bypass control solenoid valve do. I am talking about the vacuum line on drivers side on the plenum. I am trying ot track down a gas mileage problem and want to know all my compenents. I've read different things fro different cars so what does it do for this particular engine. Anyone know? Would it have an effect on my gas mileage?

[Jarrett]

You will commonly see those referred to as IABs or idle air bypass valves. The solenoid is in the black box underneath the manifold, where the vacuum diaphragm is the brass circular object you see to the right of the manifold.

The solenoid is electronically-controlled by the ECU to open at a given RPM. If memory serves, it was somewhere around 3900 rpm on these cars. Someone will correct me if I'm wrong. It opened up a second set of runners just below the plenum in an attempt to double the volume of air that could be extracted from the plenum when the secondary valves were opened. Leaving them open all the time will cause a lack of turbulence in the lower RPMs because the engine is not drawing enough vacuum to maximize the full volume of both runners. So in the lower RPM range, the secondary valves are closed, and at a certain RPM, they are opened to allow more air to come through.

The only likely source of a vacuum issue, as it relates to the intake manifold, is with the paper gasket above and below the plate the diaphragm is attached to, or the rubber vacuum lines that go to the black box.

Have you tried using carb cleaner while the engine is running to find the leak?

[zedjr10]

You will commonly see those referred to as IABs or idle air bypass valves. The solenoid is in the black box underneath the manifold, where the vacuum diaphragm is the brass circular object you see to the right of the manifold.

The solenoid is electronically-controlled by the ECU to open at a given RPM. If memory serves, it was somewhere around 3900 rpm on these cars. Someone will correct me if I'm wrong. It opened up a second set of runners just below the plenum in an attempt to double the volume of air that could be extracted from the plenum when the secondary valves were opened. Leaving them open all the time will cause a lack of turbulence in the lower RPMs because the engine is not drawing enough vacuum to maximize the full volume of both runners. So in the lower RPM range, the secondary valves are closed, and at a certain RPM, they are opened to allow more air to come through.

The only likely source of a vacuum issue, as it relates to the intake manifold, is with the paper gasket above and below the plate the diaphragm is attached to, or the rubber vacuum lines that go to the black box.

Have you tried using carb cleaner while the engine is running to find the leak?

Am going to squirt carb cleaner around it tomorrow and look for a leak. So how would they cause turbulence at lower rpms. Am a little confused as they only open at 3900 or above so if the solenoid didn't work wouldn't it just stay closed all the time?

[Jarrett]

It would cause a reduction in velocity due to the increase in cross-sectional area of the two different sets of ports combined. The source of the air flow is the volume of the plenum, so when it has double the amount of runner cross-sectional area by which to travel, it will drastically reduce the flow velocity of the incoming air.


And whether or not a solenoid is open or closed when unpowered is a matter of which is made to be its default. In this particular case, they are otherwise shut. I'm not suggesting this has anything to do with your vacuum issue. I'm just answering your initial question as to what their purpose was.

[zedjr10]

It would cause a reduction in velocity due to the increase in cross-sectional area of the two different sets of ports combined. The source of the air flow is the volume of the plenum, so when it has double the amount of runner cross-sectional area by which to travel, it will drastically reduce the flow velocity of the incoming air.


And whether or not a solenoid is open or closed when unpowered is a matter of which is made to be its default. In this particular case, they are otherwise shut. I'm not suggesting this has anything to do with your vacuum issue. I'm just answering your initial question as to what their purpose was.

So there is now way it could cause a gas mpg problem or performance issues at lower rpm's if it just stay closed all the time. Like if the solenoid didn't work or vacuum was clogged. I never get above 3900 rpms anyways.

[Jarrett]

Not likely, no.

[zedjr10]

thanks for the info man.

[Fleetw00d]

If memory serves me correctly, they open at 4500 rpm. For those engines that have the bypass valve on the intake pipe upstream of the OEM filter box, that opens the second pipe at 3500 rpm.

[zedjr10]

Effen timing advanced by 45 degrees too far. My mechanic who put on timing belt obviously didn't center things up and do timing correctly. Effen 9 months looking for this issue. I have always assumed my timing is correct for the last nine months. I will never trust another mechanic about anything ever again. I wonder what kind of damage was done or does the ecu actually limit the advancement in some way. I don't hear any knock. Thank god it was only driven for about 1500 miles.