I have 51,000 miles on my 1997 grand marquis and suddenly the mpg has dropped considerably. The dealer replaced the "mass air flow sensor valve" cleaned fuel injectors and still no improvement. Any advice. Salvatore

What is the average miles per gallon you are getting? And is the vehicle equipped with Automatic Temperature Control?Edited by: MercAdvisor

I am getting about 14 MPG. Very little city driving. Yes, I have automatic temperature control. Salvatore.

Do you use the auto temp control or do you manually make your settings if you use the auto it will switch the AC on and off while driving and can draw down your MPG.. Your mass air flow sensor could be dirty but shouldnt cause much of a MPG decreaseand check your air filter

Thank you I will try manual control. The mass air flow sensor has been replaced and air filter is clean. My highway MPG is showing from 22MPG to 26 on the instant economy reading and in city it shows 20 to 21 MPG. When I calculate the gallons used versus miles travelled I average out to 15 to 17 MPG. Just a few months ago I actually averaged out to 23MPG. I want to mention about 2000 miles ago I was having torque converter "rumble" and tranmission was flushed out. My problems began after that. Perhaps you can give me more advise. Thank You. Salvatore.

Actually 17 mpg in the city isnt terrible it is actually average for those vehicles especially as we get into the colder months. I dont know where you live so maybe you dont get cold and that may not be an issue.. As for the transmisison rumble the that is a common concern for the GM/TCAR it happens as the fluid breaks down and causes the rumble between the last shift into overdrive.. Unless the transmission is not shifting into overdrive now that could definatly have an effect on your gas mileage significantly dropping it. Make sure you Overdrive off light is not on and or flashing... Did they replace the Mass Air Flow sensor or Idle air control valve? I see you said mass air flow valve it is only a sensor just making sureEdited by: MercAdvisor

They changed the "mass air flow sensor valve. Now that you mention it, I am getting an erratic shifting and it feels like the tranny is in 2nd gear and sometimes shifts into drive at 35 mph or higher with normal acceleration. The dealer mentioned to me that the fluid could be breaking down. Would you suggest I change the tranny fluid just to be sure? Salvatore I live in Syracuse, New York and it does get cold up here. Thanks again.

If you just had the fluid changed 2000 miles ago no i wouldnt recommend another transmission flush however you may want to have it looked at to see if it is shifing through all the gears

Allright I will have them check out the transmission and see what they find. I read somewhere on the net that if you disconnect the battery cables and change the battery the computer will have to reprogram itself. I am 84 years old and never heard of it before. Any truth to it. Thank you, Salvatore.

If you only change the battery the computer will hold its program and usally will for a long period of time.. That is just a myth... UNless there was some type of interference or the computer needs a reprograming for udpated software reprogramming is not necessary..