Had my 98 F150 4.6 (100k) scanned and came up with P0401 code. Cleaning out the EGR and the intake passage didn't help-except for lowering temp a few degrees. Checked with this forum and after lots of thought I went ahead and replaced the DPFE sensor, which didn't solve the problem.
I borrowed a Mac scanner (didn't really know how to use it, but got more out of it than the guy at the Zone did with his...) and got a P1408 that read "EGR flow out of range" in the KOER test.

Tried to follow some instructions on testing the DPFE sensor, but am still not sure about the results. What i read on the voltmeter wasn't even close to what the tech doc stated. Can anyone help with an easy-to-understand procedure for testing it? I bought it off eBay and want to make sure I got a good working part... and yes, it was the newer plastic model. The original was the metal type. I checked with Ford and they told me the plastic one replaced the older metal version.

Then I put 10lbs of vacuum (via a hand pump) on the EGR and it ran rough, then smoothed right out when i released the vacuum. Did not leak down, so i assume that the vac diapragm is working properly. Seemed correct, so I checked the vacuum . At idle there is a slight flutter of vacuum at the EGR end of the hose from the vac solenoid, but when i increase RPMs the vacuum doesn't increase. (finger test) Could it be the vac solenoid not providing proper vacuum? Is there a way to test the solenoid to make sure it's providing the EGR with the proper amount of vacuum when it should?

Not sure if this has anything to do with it, but I cleared the code and drove about 50 miles with AC off before the light came back on. last time I cleared the code, I got about 15 miles with the AC on before the code returned.

Any help in pointing me in the right direction would be greatly appreciated!