Check engine light on 99 Honda Accord

Code P0401 keeps popping back up. I have had the EGR valve kit replaced twice. They also replaced the gaskets and pipe kit. When this didn’t fix it they removed and cleaned the upper and lower manifold. A few months ago the check engine light was on and they replaced the oxygen sensor and catalyic converter. They are running out of things to do except taking my money. Any insight would be greatly appreciated. This is a V6, very well kept and maintained vehicle but it drives me crazy driving with this light on. Also has 219K miles on it.

“A few months ago, the check engine light came on…” WHAT was the code? It may have been something else, rather than P0401.
They have a chart to go on for troubleshooting the egr system. I have no idea of how much of the chart they have followed; therefore, what’s left?
The egr, oxygen sensor, catalytic converter seem to be fouling with something. It could be from burnt oil, or poorly burned fuel.
The engine is high mileage, and may have worn cylinders and piston rings. This could allow oil to be burned. Worn spark plugs could have misfire (which you WOULDN’T feel unless it were extreme). Check engine leak down and do an engine vacuum test. Hopefully, some mechanic knows how to do these tests in a diagnostic manner…more that just getting raw numbers.
Whatever is telling the engine computer that the egr flow is insufficient may be mistaken, etc.

Thanks for the comment. It makes sense to me that the mechanic is probably not following the flow chart. The car had a major tune up done last year and uses synthetic oil which is changed every 5000 miles. What happens when fuel doesn’t burn properly and how can you prevent it?

Have you noticed any change in you gas mileage? Are you loosing any oil? These would be related and could lead to the answer you seek.

Nope, the gas mileage has not been compromised and is not using any oil.