Egr

I own a 98 S-10 2.2L. The SES light has been on for about a month and I ran a test the other day and it read 'P404 EGR perf CKT Range' I don't speak computer, but I think it's EGR performance the rest I have no clue. I asked a couple parts specialists they informed me that replacement of the EGR valve is an option but at 200 bucks a piece it's a risk because it may not solve the problem due to carbon buildup in engine. So what I am asking is what can I do to fix this without risking a couple hundred bucks.
Thanks.

Code 404 is the EGR valve pintel position stuck open.

First step is clear code and see if it comes back.
Check wiring and plugin.
Pull egr valve and check for a carbon/carbon ball holding pintel valve open/on position.
The only way to check the egr valve performance is to use the egr test on a engine capable scanner.
With a scanner you can read out egr pintel positon and desired position.
They should match.
Also a good engine scanner will open and close and test egr valve.
MT