Toyota Repair: check engine light, vacuum modulator, vacuum gauge

Question
I have a 99 toyo tacoma 4cyl. 2.7 auto trans. w/118k miles my check engine light
has been on the code reads "po401 egr valve, insufficient air flow".  Thus far I
have: Replaced the manifold, new cadalitic conv.  new egr valve and cleaned the
pipe from manifold to egr valve,replaced the vacuum modulator on top of the egr, and chk eng. light still on. and still reads the same code! Pls help.
what should I do?  

Answer
Kevin,

I am going on memory here so I hope your truck uses this same system. There are 2 vacuum lines from the throttle body to the EGR modulator.  Check the tubes on the throttle body where those lines connect. They are known to carbon up inside the tube and throttle bore.  Next, use a vacuum gauge on those same ports, start the engine. There should be NO VACUUM with the throttle closed. As soon as you open the throttle to part throttle it should have some vacuum applied.  

If all that checks out ok, move to the output side of the modulator and check for vacuum again at part throttle.  Now follow that line and I believe it goes to a VSV (vacuum switching valve). You can apply power and ground to the valve and check that it is conducting vacuum. Also, one side of the VSV is vented when it is closed, this side goes to the EGR valve itself.

If I got you confused or you need more help just email me directly at Timthecarguy@earthlink.net