1997 Honda Accord EGR & Check engine light issues?

I have a 1997 Honda Accord EX-V6 with about 165K miles on it. Back in Nov, I got the check engine light on and took it to Tire Plus and they determined that it was the O2 sensor, which they replaced. Everything was fine till about end of Jan when the light came back on. Took it to a different mechanic and he determined that one of my cylinders was misfiring. He did a complete tune up (sparks, rotors, caps, wires, fuel filter, etc). But a few days later the light came back up again. This time it was EGR (code P0401-Exhaust Gas Recirculation (EGR) Insufficient Flow ). The mechanic cleaned out the EGR value and everything else and reset it. Well after a week, the light came back AGAIN. Since I am out of warranty, the dealer was going to charge me to replace the EGR valve. So I bought the EGR unit seperately and had it installed. The computer was reset, but about a week later the light kept coming back on with the same P0401 code!! Even the PCV valve was replaced. What could be the issue?|||It could be something simple as a vaccum hose becoming disconnected or leaking. I remember having an EGR code on my Toyota Highlander and after finding a disconnected vaccum tube and reconnecting it, the code went away after resetting it. So inspect the vaccum hoses that conect to the sensors in your engine. Vaccum hoses are the small hollow tubes that carry air, not wires.