Toyota Repair: check eng. light, plenum chamber, intake plenum

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, and it still reads the same code! Pls help. what should I do?  

Answer
Was the EGR modulator valve also replaced when the EGR valve was replaced, EGR valves themselves rarely cause a problem, the most common cause is the EGR modulator valve connected on a bracket on the EGR valve, another common problem is the EGR vacuum switching valve(VSV) located under the intake plenum chamber, in rare cases the EGR gas temp sensor can cause the problem , make sure it's electrical connector is connected, the sensor is on the lower part of the EGR valve.