I just learned something today, I had the same exact problem with the exception that I did the work myself. I had replaced the EGR Valve and the PCV Valve. And the problem persisted. Until today, I solved it by watching a few YouTube videos about cleaning out the throttle body and EGR port, right inside the intake. The bad EGR Valve may not have been bad, but the carbon build up inside the the intake, behind the throttle body was my issue. I purchased a can of carburetor and choke cleaner. I started by removing the throttle body, it was not very difficult to get to.
I needed a straight screwdriver, a pair of pliers, 10mm socket, 13mm socket a ratchet and a small extension. There are a lot of videos on how to remove it for just about any car. I removed the plastic sensors on the sides of the throttle body with a torx driver, and cleaned the throttle body with a the spray cleaner, a tooth brush and a lintless rag. Then I dug into the port just inside the intake, behind the throttle body. It looked like a fresh ant hill made of carbon, completely blocking the hole for the EGR valve.
I picked at the carbon with a hook/pic, (I felt like a dentist) then sprayed it with carburetor cleaner. I also removed the EGR valve before I started picking at it, I used a stiff but bendable wire to pick through the port all the way back to where the EGR valve bolts on. I spent about an hour cleaning it all up. Finally I blew it out from the hole back with an air compressor. I put it back together, cleared the code and drove it for about thirty minutes. No codes, no check engine light (previously a ten minute trip would turn on the check engine light). I am quite confident that it will not come back for my time with the vehicle. I have similar mileage as you, right around 140,000 miles on a 2004 Impala 3400.
I hope this helps your or someone else.
Thursday, January 19th, 2017 AT 8:12 PM