2005 Mercury Montego Lost seven miles per gallon

2005 MERCURY MONTEGO
140,000 MILES • 3.1L • 6 CYL • FWD • AUTOMATIC
Avatar
KATE2001
  • MEMBER
  • 11 POSTS
At about 135,000 miles, gas mileage started to drop from the usual 26 mpg. I have a 19 gallon gas tank and was getting 494 miles per tank. Now it is down to 350 miles per tank. The dash shows I am getting around 19 miles per gallon. At 100,000 miles, I changed SPARK PLUGS, OXYEGEN SENSORS. I change oil every 5,000 miles. Good tread on tires and rotate tires at every oil change. I have changed gas filter at 132,000 miles. At 125,000 miles I had both front struts replaced. Change air filter as needed. Everyone I talk to says it is the winter blend of gas. I have a hard time swallowing a seven mile per gallon drop in gas mileage. This vehicle has no analyzer codes being shown. Runs great. Automatic shifter works fine. Has the same pick and go that it had back when I bought it in 2008. Any help would be greatly appreciated.

Thank you
Jan 20, 2014 at 5:46 PM
Advertisement
Avatar
TY ANDERSON
  • CERTIFIED EXPERT
  • 719 POSTS
It is true that winter fuel doesn't pack as much energy as the summer fuel.
However, there are other reasons for lower fuel economy. Colder ambient temperature places a greater demand on the engine's cooling system. The cold temperatures causes the engine to consume more fuel to maintain the operating temperature. Using the heater also cools the operating temperature.
Low tire pressure, dragging brakes, out-of-alignment, air condition (defogger uses the air conditioner to reduce moisture inside vehicle), a weak or coated mass air flow sensor will give inaccurate reading to vehicle's computer.
It looks like you've maintained your vehicle well so I wouldn't suspect that there is an issue. Unless this continues into spring.
Hope this answers you question.
Jan 20, 2014 at 7:40 PM
Avatar
KATE2001
  • MEMBER
  • 11 POSTS
My next question was going to be the THROTTLE POSITIONING SENSOR (TPS). I did forget to mention that there was a recall on the throttle body that becomes dirty and requires the throttle body to be cleaned and the PCM to be reprogrammed, which I had done around 135,000 miles by the dealer. If the TPS is bad, I am unable to buy a TPS separately for this vehicle. The dealer wants over $600 for the throttle body w/ TPS and the auto parts store wants over $300 for same. Would I be taking a chance to buy the TPS at the local junk yard?
Jan 21, 2014 at 6:03 PM
Advertisement
Avatar
TY ANDERSON
  • CERTIFIED EXPERT
  • 719 POSTS
The electronic throttle body is all one part there are no serviceable parts and thus the high cost.
I found the customer satisfaction bulletin about the build up on the throttle body. According to the bulletin this build up was not accounted for when the programming went into the acceleration system. This issue may or may not cause the check engine light to illuminate and engine idle RPM variation. It effects the idle quality only and could decrease fuel economy but only if the check engine light is on.
I wouldn't consider the throttle position sensor as the cause of reduced fuel economy. It usually causes unusual drive ability issues or causes the engine not to start. However, this is an electronic throttle body and the TPS is monitoring the throttle motor and relaying the throttle plate position to the vehicle's computer. In other words when you press on the accelerator pedal is the electronic throttle body motor doing what the driver is requesting. If it is not it is going to flag a warning or check engine light.
Jan 21, 2014 at 7:58 PM