I have lost a lot of gas mileage all of a sudden. The brakes are not dragging, motor runs smooth, transmission shifting and working as always,newer plugs, good clean air filter, tires are at 35 lbs. I don't have any codes but my mileage dropped from 30 highway / 26 in town to 26 highway / 17 in town. I am on a trip now and I can not figure this out. If anyone has any ideas please let me know.
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Welcome to the site, many possibilities, a tank of bad fuel? Possibly!
Check your oil level.

 

I have went through 3 tanks of gas. I changed the oil about 3 weeks ago and it is still on the full mark. I have searched for fuel leaks and found nothing and don't smell gasoline. I am at a loss on this one.

 

"newer plugs"

What plugs did you use?

 

Good question? Are they AC Delco 41-103 Iridium plugs?

 

Alcohol content of the fuel.

 

Dirty throttle body and MAF sensor?

 

I don't remember now but they were the same as the original ones I took out.

 

I'm going to clean them tomorrow and pour in a can of Sea Foam.

 

I think maybe but I am on a trip right now so I can't check my records. The mileage was fine for a long time after I changed them though. This just happened all of a sudden about 2 weeks ago. I tried reseting the computer also. I drove it 120 miles today on the Florida Turnpike at 70 mph and got 23 mph.