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A few days ago I changed the spark plugs in my 2010 Mazda 3 2.5L. I've been watching the fuel economy display, and it seems to be reading much higher under acceleration or going up hills. When cruising, it seems to be about the same as it was before. I put in iridium plugs and gapped them to spec. Any idea about what could be wrong is much appreciated
 

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try to unplug your battery for about 15 minutes. Then plug it back in and drive like how you usually drive. Your car ECU will re learn how you drive that fuel economy will adjust itself.

If you haven't yet, take your throttle body apart and clean it. I have 136k miles on my 2011 Mazda3 and I have cleaned it twice already. Both times had alot of carbon build up.
 

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Discussion Starter #3
try to unplug your battery for about 15 minutes. Then plug it back in and drive like how you usually drive. Your car ECU will re learn how you drive that fuel economy will adjust itself.

If you haven't yet, take your throttle body apart and clean it. I have 136k miles on my 2011 Mazda3 and I have cleaned it twice already. Both times had alot of carbon build up.
I disconnected the battery when replacing the plugs, but ill do it again.
 

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Discussion Starter #6
I thought I should leave an update for anyone who finds this thread in the future. The aftermarket plugs I purchased were not the exact same size as the OEM Mazda ones I took out, the porcelain part was a little bit bigger. I went to the dealership and purchased OEM plugs to make sure I got the right ones. After putting in the OEM plugs, it still felt like the fuel economy computer was showing worse fuel economy, but in reality, I'm getting the same mileage I was before I changed the plugs, so I am probably just paranoid. That or the engine is running differently now that the plugs have been changed and the computer is accounting for that. Also worth noting is that I torqued my plugs to 15 ft/lbs to make sure they were tight enough, I found a thread somewhere saying the correct spec is 8-10 ft/lbs, but this felt awfully loose to me.
 
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