help me with Unexplained change in F 150 MPG

i have a 1998 f150, with a 4.6 V8. When i purchased it (used, about 4 months ago) i had it checked by a mechanic who is also a friend. it was given a clean bill of health, and had all the fluids changed. I
added a K&N filter, and have kept the oil and oil filter changed on schedule. The car is stock.
I used to get 20 mpg with ambient temperatures 100+ in the day, at elevation 200'. I moved and now am at 10 mpg in 60 degree heat at sea level (and by the beach if it matters). My daily driving now requires a greater amount of idling commute time in traffic, but otherwise my habits are unchanged.
I have checked for obvious problems (tire pressure is nominal, air filter is clean, no pool of gas exists under my parked car, I have ruled out the siphoning of my gas, and I always check my emergency brake).
I have unhooked the battery cable in an attempt to reset the computer and change the driving profile, but I am thinking this will be fruitless.
Does anyone have any idea what might be wrong?
Thank you
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Extended idling time in traffic is death on gas mileage. The engine is burning gas, but the vehicle is going nowhere. It's too bad you disconnected power to your computer system. When you did that, the RAM was wiped out. The RAM in the computer system is what the computer uses to optimize the engines' systems given the driving history. When the RAM is lost, everything reverts to the factory default settings for all the engines sensor systems. The defaults are for when the vehicle and all its systems were brand new. Over time the RAM built a driving history and could compensate for any changes in the systems. Older vehicles usually don't perform very well on factory default settings. Eventually a new driving history will be built, but until that data base is built, the vehicle probably won't do very well. The RAM was also where any trouble codes were stored.....those were wiped out also. The codes might have been a great help in determining what, if anything, might be wrong/going wrong. It might be a good idea to pull your plugs and see what they look like.....or install new plugs just for grins. Look into your computer for any trouble codes present now, or if you don't know how, learn/get some info on how to do that. You will also learn how to properly 'reset' the computer system so the RAM data base is kept intact.
Hope some of this is of use to you......
Dave S(Texas)
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DING DING DING.
We have a winner.
How many MPG to get when idling in traffic? 0?
Jeff
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eat411 opined in

The others are right...
Just think about your problem in terms of time spent idling / accelerating as a percentage of total time running And compare it to the previous location
My wife used to have a 100 mile daily commute, her mileage stayed at around 27 mpg.
She transferred to a local office to avoid that and now gets around 18..
Abetting the drop is the time she sits in the car at lunch with the a/c or heater running.,,, which caused her mileage to drop to about 24 to 25 for the distant job.
BTW...I have NEVER seen new plugs add more than 1 mpg even if the old ones were worn to the point of occasional engine miss... and that's OBVIOUSLY worn
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