99 malibu fuel mileage

[ia31638]

99 malibu, 147000 miles, 3100v6, 58000 miles on tranny. My fuel mileage only averages at 17mpg city and highway combined. Recent tune up less than 500 miles ago, OEM plugs and wires, and upper and lower intake gaskets all done at tune up. Car starts and runs great. I've only had car for about 2 months and my work car. Bought this for fuel mileage driving to work. Guess i was wrong there. My 3/4 ton dodge gets 18 mpg on the highway. Whats up with this car.

[dpalomaki]

Check to be sure it is reaching normal operating temperature within 5 miles or so (about 1/2 on the gauge). If temp is not being reached, you may have a stuck open t-stat and that will hurt MPG.

A lazy O2 sensor (the sensors at the engine, not the one after the cat con) can also result in a in MPG. At 147 K miles they may be getting old and tired, but not to the point of setting a code.

Neither item would effect driveability significantly, but would hurt MPG.

Depending on where you are, winter blend gas hurts MPG by about 3% as well (compared to spring/fall).

[ia31638]

Well i found a broken wire for the intake air tempertaure sensor. I purchased a scan gaugeII tool and found the intake air temp sensor was reading -39 (below zero) when it was actually 50 outside. Pretty sure the car was running quite rich. It never set a MIL light though. I'll check gas mileage for a week and see if it helps.

[ia31638]

Took it on a 90 mile interstate round trip with a little in town driving. got 26 mpg. Wish it was closer to 30mpg.

[jyount]

That is a good improvement though, bet you found the problem.