New sparkplugs = Bad Gas Mileage?????

[nolava]

hello fellow avalon lovers, i just changed my sparkplugs in my car and I usually get 300 miles before the gas light comes on, and now i'm getting 260 before the light comes on. I replaced with the ngk iriduims like everyone suggests. I even went to as far as cleaning the MAF sensor with carb cleaner. I changed the air filter, checked the tire pressures. Could it be the O2 sensors? The car runs fine, infact i think it runs smoother and stronger. What could be the problem???? any ideas?? thanks guys

[Nad1370]

Try another tankfull or two just to verify it.
Could be low quality fuel.

[ChiTDI]

You could be enjoying that "smooth and stronger" a little bit too much !

[TrailDust]

I know this may seem a stupid question, but it's often the most obvious things that get overlooked. Did you ensure the proper gap was set with the plugs before installation?

FYIGMO

[aznstylez]

Originally Posted by nolava

hello fellow avalon lovers, i just changed my sparkplugs in my car and I usually get 300 miles before the gas light comes on, and now i'm getting 260 before the light comes on. I replaced with the ngk iriduims like everyone suggests. I even went to as far as cleaning the MAF sensor with carb cleaner. I changed the air filter, checked the tire pressures. Could it be the O2 sensors? The car runs fine, infact i think it runs smoother and stronger. What could be the problem???? any ideas?? thanks guys

did you check your PCV valve to see if it's working or not? And like TrailDust asked, "Did you ensure the proper gap was set with the plugs before installation?"

[nolava]

Problem Solved!!!! after researching on this site and a few lexus forums, I found that i had forgot to reset the ECU after cleaning the MAF sensor and the sparks. Now my gas mileage is back to normal.
as far as gap goes......these are iridium sparks, i heard somewhere that your not supposed to adjust the gap on iridiums?

[aznstylez]

Originally Posted by nolava

Problem Solved!!!! after researching on this site and a few lexus forums, I found that i had forgot to reset the ECU after cleaning the MAF sensor and the sparks. Now my gas mileage is back to normal.
as far as gap goes......these are iridium sparks, i heard somewhere that your not supposed to adjust the gap on iridiums?

Weird, I have never heard of having to reset the ECU after cleaning the MAF sensor. Are you sure everything is back to normal because normally it takes a few days for the ECU to reset itself back.

[avalonshoe]

how would u reset the ecu? take out the ecu relay/fuse? or unplug the car battery for some time?

I had my sparks changed after seeing the compression leaking through and clean the MAF sensor myself. On a road trip i get around 410-440miles on the full tank. I live two miles from I-10 so mostly highway miles on the car.

[Eurobob]

iridium plugs are pre-gapped. i would love to see anyone who can gap and iridium plug and not break the electrode. Reset is weird. never heard of that either. i get about 400 on a tank if i am running 93+ octane. 310 if lower than 92 octane