About 4 weeks ago the check engine light in my '01 Monte SS (3800) came on and Autozone told me it was an EGR valve error. I purchased a new one from them and installed it. The light turned off, hasn't come on since then, but I've noticed anywhere from a 3-5 mpg drop off in my average fuel consumption since I installed the new EGR valve. Any thoughts? Is it possible that I bought a poor quality replacement part from Autozone (I've heard poor reviews of their parts before)? Would it be reasonable to believe that part is the reason why my mpg has dropped 17%?
The car has about 98,500 miles on it and I have yet to replace the spark plugs (suggested at 100,000). I'm going to throw some Gumout fuel system cleaner in it on the next fill up, and replace the air filter this evening (hasn't been done for awhile). I replaced the fuel filter around 65,000 miles.
Any ideas would be appreciated.