I have a 1999 Mercury Mystique with around 177,500Km. I had an EGR valve insuficient flow error code so I change the EGR valve and the check engine light is still coming ON. The old valve had heavy carbon build-up and that's what I thought the problem was but it still tells me insuficient flow. I've tested the new valve and it works properly. Me personally, I don't think the vacuum is pulling hard enough to open the valve. What can I do?
Did you have your throttle body cleaned out, check the valve hoses, when replacing the egr valve, you should always replace existing hoses. Mercury's are known to have heavy carbon build up in there vehicles.