VSV / EGR / Modulator purpose

[deddy]

1994 Camry LE with 2.2 liter and automatic

What is the purpose of the VSV valve? This is the part that is bolted to the head below the intake manifold (at the rear of the engine). Vacuum lines #1 and #2 are connected to it and the wiring connector seems to apply 12 volts in order to open and close the valve.

'Course, I see that the VSV vacuum lines connect to the EGR modulator, so I assume the VSV controls the EGR in some way.

But exactly what is the purpose of the VSV?

And what exactly is the purpose of the EGR - I understand it feeds exhaust gases back into the intake, but when is this done? During engine warm-up, or always during normal engine operation? I have removed and cleaned the EGR and I know it moves normally.

And while we're at it.... what is the purpose of the EGR modulator? Does the modulator cause the EGR valve to open to a greater or lesser amount (by increased or reduced vacuum)?

The reason I ask is, I have found that one vacuum line is disconnected from the VSV, because the plastic pipe (nipple) is broken off. So I merely removed the VSV and connected the #1 vacuum line to the #2.

Car seems to run fine.

What functionallity am I foregoing?

Thanks

Doug

[deddy]

I found some helpful information on EGR / VSV / Modulator here:

http://www.autoshop101.com/forms/h61.pdf

[JohnGD]

The autoshop101 article is good. The vacuum modulated EGR valve is a really old design, but basically trying to match EGR lift according to throttle valve position and vacuum at the throttle body ports.

These days various sensor information are used to control digital EGRs using stepper motors. Anybody still cleans EGR valves? Not.

Engines with exhaust side variable valve timing dont' need EGR valves. And some cutting-edge engines with Continuously Variable Valve Lift do not use throttle plates to accelerate. They use -- you guessed it -- variable valve lift!!! etc etc