No, he means the Exhaust Gas Recirculation (EGR) passages are clogged
with carbon.

What was the exact error code? P0401? P1491?

If you have a V6, there is a known issue with the EGR. It is covered by
TSB 99-085. Doesn't save you any money, but will fix your problem.

The 100 mile thing sounds right, the $800 thing does not. Does he plan
to spend six hours on this?

My check engine light has ben on for a couple of months now.  I took the car
to get it inspected and they told me it is an automatic failure because of
the CEL.  I took the car to a mechanic and he said that the air intakes are
clogged with Carbon.  He said that he is going to clean them out and replace
the valve associated with it.  Cost $800.  I asked him if he would go ahead
and inspect it after the fix.  He said I had to drive the car for 100 miles
or so for the fix to register and pass inspection.  Does that sound right?  I
know nothing about cars.