EGR issues

I have a 1999 Nissan Maxima with 117,000 miles, V6 engine. About a month ago, my car starting making a loud noise (it sounded to me like the muffler). I took it to the repair shop, and they determined that the EGR valve needed to be replaced. That fixed the noise problem, but a day later the service engine light came on. I took it back to the shop, they hooked it up to the diagnostic computer and said no problems were detected, so they turned off the light, chalked it up to some air getting into the system, and sent me on my way. Another day later, the light came back on. I took it to another shop, they hooked it up to the diagnostic computer, came back and informed me that the EGR valve needed to be replaced! I explained that it had just been replaced, so they said they would replace the EGR temperature sensor and see if that fixed the problem. They explained to me that the diagnostics pointed to the EGR system, so they would have to replace the most common components one at a time until the problem was fixed. The sensor that they want to replace was out of stock, so it has not been installed, yet. Does this sound like the correct procedure to you? Thanks for the advice.