Keep your fingers crossed for a low-tech solution.

At 168K miles, if your resonator and intake manifold have never been cleaned, your problem may simply be internal gunk--especially gunk that's clogging the butterfly valves. The EGR valve dumps particulate-rich exhaust back into the intake, which builds up and restricts flow in the intake tubes (think: atherosclerosis).

You can remove and clean these yourself, although it's a time consuming and rather messy job (I know from experience). Better to take them to an engine shop and pay a few bucks for a good solvent dip or steam clean.

Also check electrical and vacuum lines/connections to the EGR valve and the butterfly valve under the manfold.

babymog is generally correct: several (3) start cycles without a recurring error can clear a CEL. But of course, the key word here is "recurring."