low flow does not mean the egr valve
isn't working. It means the MAP sensor did not read the intake vacuum change it was looking for when the egr was commanded on. Here's on reason that may cause this problem. The PCV system will allow oil to be drawn up into the intake very close to the egr port in the intake. That oil, over time, will mix with exhaust soot and plug up the egr passages.
(example: removing throttle body and EGR valve
will provide access to both ends of passageway. Removing vacuum tee at the top of intake will allow a straight line of access for cleaning with a long screwdriver etc. The crooked passage over to EGR was cleaned with a piece of speedometer cable or something flexible.)