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Q: egr valve..bad gas mileage on 2005 Mercury Monterey

I had code p0401 on my van. I cleaned my egr vavle with carb cleaner and reset code by disconnecting negative battery cable. I put everything back into place and now I am noticing horrible gas mileage. It has been 2 weeks and no code, but bad mileage. Why is this going on? thanks.
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I wonder if you have a vacuum leak at the EGR if it was just "off". A vacuum leak picked up by the computer in your car would indicate a lean mixture and this message sent to the Oxygen sensor to the computer would be interpreted by the computer and the computer would richen up the fuel mixture. The most efficient was of figuring out the exact cause and effect is using a professional grade scan tool and reading live sensor data off the tool rather than doing intrusive sensor testing at each sensor. Scan tool displays a lot of information but is only as good as the person interpreting the information.
If your EGR valve is stuck open it will dump more exhaust into combustion chamber and that could potentially reduce your mileage, but in that case your ECM should give the same error code
they are 4 bolts, 2-12mm at the top, and 2-10mm at the bottom, the hard one is the right-bottom one you have to use small ratchet in between the manifold, but not too hard.
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