EGR Valve Question

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.
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I would have changed those plugs long ago.
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80 Knight wrote:

Wow, that's for sure. And I bet the O2 sensors are going bad. 100k is pushing it.
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100,000 miles is the recommended service interval for Iridium spark plugs.
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No offence, but the recommended service interval is based on a certain type of driving. If the car is displaying signs that a tune-up is required (and, this car is only 1500 miles away from the recommended tune up time anyhow), a tune up should be done.
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Most cars today will go 100k on a set of plugs. Were the ports to the EGR cleaned? They usually plug up more than the valve going bad. The 02 sensers can be checked with anOBDII tester. They are monitered closely with the computer and will throw a code before causing that kind of fuel loss. Check the misfire counters with the OBDII tester as well as other sensors. I would start by cleaning the EGR ports and verify you installed the correct valve and correctly.

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FWIW, I *have* had to replace the EGR on my '96 cavalier...twice.
The first replacement was an aftermarket "fits all models" job that required some fiddles to make it fit the 2.2l OHV on the cav. Second replacement came a year afterward with the replacement specific to the cavalier and almost identical to the OEM unit (which I still had kicking around the shop). I asked the AP store what was up and they said they stopped carrying the "all in one" units due to poor performance.
B.
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Even though you 'heard' bad reviews about AZ, you spent your money anyway? The probability is high about AZ replacement parts being of poor quality. EGR valves are usually vehicle-specific and 'generic' units won't work well with the computer systems.
Dave S(Texas)
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