P0402 code, how urgent?

My Tacoma:
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

 

P0402 is for excessive EGR flow detected. This is an emissions related code. If there actually IS too much flow it can cause excessive emissions and possible stumbling and hesitation. Can it wait a month? Possibly. It is hard to tell because we don't know if the fault is a true failure, or a sensor problem. If it is a sensor problem, then you could wait, if it is a failure, then it may get worse.