Hello, I am new here but would really appreciate some help. Like the topic says I have a 1997 Pontiac bonneville with a P0401 DTC Egr Flow Insufficient check engine light is on. I installed the revised upper intake plenum last summer and the car ran great until a few weeks ago, the p0401 DTC was generated. The car now runs rough and feels like it is skipping.I have heard that I should pull the egr valve off the motor and see if it is plugged aswell as the tube. Should this be my first step? I am hoping that someone else here has ran into this and will have some solid advise for me. Thank You.