1999 PreRunner 2.4L auto, 157K miles.
A couple of weeks ago the CEL came on. The truck seemed to be running as normal but I went ahead and took it to my mechanic (not a toyota dealer). He said it gave an EGR code so they checked the system and found nothing wrong, suspected a stuck valve. They cleaned it and reset the CEL. A couple of days later the light came back on, still seemed to be running just fine.
I borrowed a diagnostic scanner and got code "P0402" suggesting the same thing.
Im not much of a mechanic at all so fixing it myself is probably out of the question. How urgent is it that I get this fixed? Can it wait about a month? Like I said, it seems to be running just fine, no loss of power or anything. I don't put very many miles on this beast but I do really want it to last another few years.
Any thoughts? Thanks so much