EGR, clogged valves, bad exhaust

My car is experiencing exhaust problems. When I took it to a local shop for a free diagnostic I was told I needed a new EGR. So I had that replaced (at a separate garage where I got a great deal on labor).

The next day, as I hit 75 on the highway, the ‘check engine’ light came on again. I took it back to the first garage for another free diagnostic. They said that even though the EGR had been replaced, the valves around it were likely clogged but only a proper, computer diagnostic ($100) would be able to pinpoint the problem.

I've already spent $400 in recent repairs so my question is: Can I safely and properly clean these valves myself?

Thanks in advance for any advice you all have.