Originally Posted by Trainwreck
The EGR valve was passing all the tests because it was not broken, it was just the wrong one for my application. What an ordeal! But I'm happy- the truck is running like it should and my blood pressure back down to a reasonable level.
Look at the "faulty" egr valve where the vac line attaches. The right one will have a pinhole sized restriction slowing the vacuum while the wrong one will have a wide open vacuum port. The wide port causes what you're describing as once the EGR gets a signal, it slams open causing the stumble. The right one will use the vacuum restriction while the aftermarket ones will also use washers to regulate the exhaust flow at the base of the valve.
As for your tech buddy, the backpressure type egr valves are more sensitive with more backpressure. Less backpressure and the valve is less sensitive. The magnaflow might cause a code 32 (worst case, not likely as in nearly impossible scenario) but won't cause the valve to work as he described. You've just witnessed a "parts tosser" tech. Thump him for me.