I was helping a couple of owners to diagnose EGR problem. One turned
out to be the VSV that operates the EGR valve, the other turned out to
be dirty throttle body with vacuum ports plugged up. Here were some
exchanges from then, see if this helps:
The modulator usually do not go bad, neither does the EGR valve,
although it may get blocked by soot.
Air blown into the hoses from the modulator's Ports P and R into the
throttle body should flow freely into the throttle body.
To be tested:
Test 1 -- To rule out VSV as the problem.
Test 2 -- Whether the EGR modulator is indeed the culprit.
Step 1 for VSV:
1A. Disconnect hoses from Port Q at the modulator and at the EGR valve.
This leaves VSV with two long hoses to test. Mark them so you can put
them back in the right places.
1B. With the engine cold, stopped and ignition ON, Port Q hose leading
to the VSV should hold vacuum, use about 15". And blowing through the
EGR valve end of the hose you will hear air coming out of the VSV
filter, which will help you locate it as well.
1C. With the engine warm and at 2500 rpm, Port Q end of the hose should
loose its vacuum automatically as VSV is opened. This means the Port Q
hose now opens all the way to the EGR valve end of the hose.
This confirms VSV and its control circuit is working; otherwise the VSV
or the vacuum hoses leading VSV to are leaking or VSV is not energized.
Verify proper electrical connection to VSV. Clean or change the VSV and
Step 2 for VSV while also checking out modulator:
2A. Now your engine is warm in diagnostics mode from Method 1, tee Port
R of the modulator to the MAP hose (getting full engine vacuum now).
2B. At 2500 rpm, you should measure about 13" at Port Q of the
If the numbers are the same at Port Q of the modulator and at the EGR
end of the hose, then VSV is working.
But if Port Q of the modulator shows a higher vacuum than at the EGR
valve, then the VSV or the vacuum hoses leading to VSV are leaking.
Clean or change the VSV and hoses. In this case of higher vacuum at
Port Q, a direct hose from Port Q to the EGR valve should cause the
engine to run rough in the diagnostics mode at 2500 rpm. If not, you
may have problems at both VSV and modulator.
Josh Rogers wrote:
> An OBD2 scan has revealed that my check engine light is being caused by
> "Insufficient EGR Flow"
> Looking at the suggestion found at
> http://experts.about.com/q/832/4142992.htm?zIr=5#r i tried pulling the
> modulator (which I think is the plastic piece that has 1 vacuum tube
> going to the EGR, one out the bottom, and two more out the side going
> who knows where) I tried blowing air into the bottom of the modulator.
> Air goes through regardless of which one of the upper vacuum holes I
> cover. I'm guessing its broken.
> I've called my favorite parts house, and they can't find anything named
> "EGR Modulator Valve" or anything similar. Am I calling this the wrong
> thing? Am I going down the right path here?