Lincoln/Mercury Repair: Mercury Grand Marquis, mercury grand marquis, couple beers

Question
Hello, I have a 2001 Grand Marquis LS....I have 2 engine codes popping up that have caused me to fail emissions. PO401---- EGR insufficient flow detected & PO402---- EGR excessive flow detected.

I read on a Mercury message board that 95% of the time if you get both codes, it is the DPFE sensor.

OK, what do you think? does this sound accurate?
And, how expensive of a fix is this?
Is this something I could fix myself? (long shot since I am not very car engine savy)

Thanks
Rich

Answer
Hi Rich,

I have had this before and found that the EGR valve was full of carbon in the orifice tube. After cleaning it out, it ran beautiful and codes went away. I would definitely try this first, zero cost. If you don't find anything unusual with the EGR then my next step would be the Differential Pressure Feedback EGR sensor. You might be able to do this, the book time is only 24 minutes. So grab a couple beers and have at it! They don't give me the price of the DPFE but an EGR is $73.