my mileage dropped from around 32 on the highway, to about 22.

any ideas? filter done about 3,000 miles ago, plugs about 12,000-15,000
i cleaned my IAC valve yesterday, not sure if this affects mileage, but idle was funny.

 

o2 sensor?

 

Did you make sure that all the harnesses coming out of the IACV were put back? How many miles do you have? Like MrDuck said, O2 sensors. They usually go bad around 100k miles, some before some after. Has your TB ever been cleaned? Also try to shoot some Greased Lightning for your fuel system. The bottle is about $8 (ouch) at Advance Auto or PepBoys but it's worth it, I used it last year and I gained alot of response and a slight increase in fuel economy since then. Good luck

 

yeah well i meant to say that i cleaned the IAC valve after the trip with the bad gas mileage. yeah maybe o2 sensors, i have about 120,000 miles, and i dont know if they have ever been changed. i have had the car since around 106,000. throttle body cleaned 5,000 ago.

 

I have similar problem. My mileage dropped significantly in the last few month. I had o2 sensor and knock sensor codes. Since then I changed both front o2 sensors, knock sensor, fuel filter, spark plugs, air filter, cleaned TB. But it doesn't help a lot.

Anybody, please help to ucover this mistery.

 

i barely get 300 miles on a full tank. i got 90,0000 miles. what you getting?

 

well i havent gone a full tank since the drop in mileage. just went on a long trip, and refilled when i got back.

i dont have any codes. i will wait and see what i get out of this tank.

 

that is like 16 mpg. seems to me that is really bad. do you drive crazy around town?

 

Last time I've got 320 miles on a tank and the car stalled 10 meters away from a gas atation.
This spring I could easily get 400 miles.

Car is little bit over 100 000 miles.

 

well i went on another trip today. 20MPG!! highway miles with cruise control!
does the O2 sensor throw a code?

what kind of mileage do you guys get?

 

300 miles a tank, thats what I get... and I use premium gas... its killing me

I have 80,000 miles on my car...

I need to get a new muffler, will that help?

I dont know what I need to do but this gas mileage is killing me....

 

i havent done any engine mods nor do i drive like a race demon. seems like im getting less and less miles every fill up. car runs great too. better then when i first bought it with 45,000 miles on it. i drive mostly freeway too.

 

I cant anyone hasnt come up with the knock sensor... thats usually the cause of bad gas mileage in a case like this.

 

well no code, did the resistance check, and it actually is one i put in there myself less than a year ago.
i guess it is possible though.

 

winter forumla gas???????or lead feet

 

Fat g/f?? I dunno then

 

This is a perfect example of why everyone should have an OBD-II scan tool or have access to one cheaply. There is no point in guessing in the dark on these types of things. You spent over $300 and the problem is not fixed. My guess is that your rear O2 has been hit by a rock and is dead. Take a look at it. If it is at all deformed you can bet its shot. They are very sensative. If you had a scan tool you could have looked at the values coming out of all the sensors and purchased the replacement part acordingly. My money is on the O2 sensor for both of you. The final test is your top speed. With a bad rear O2 and N/A auto will top out at ~125MPH.

 

Yes i barely get 300 to the tank as well. I just did a full tune up. Fuel filter, air filter, spark plugs, oil change/oil filter still i get the samething it is possible that it is the o2 sensor but shouldnt i be getting some codes ? I get no codes and i have 113k miles on my car. I dont race cuz i have an automatic but i would like to know why my gas mileage sucks

 

well i top out at 115. speed limiter.

 

Well, get an OBD-II reader.

 

I have been getting pretty sh!tty gas mileage lately and the other night on the highway I just kept accelerating in 5th gear and got to about 125-130 and I felt a hard jerk so i slowed down right away. I'm not sure if i could have gone faster but I wasnt going to take a chance. Does that mean my O2 sensor is shot?

 

why is that when theres ever some problem some one has to jump in with the knock sensor...

i get terrible mpg and i have new 02's and a new ks

 

has it always been so? or did it go down at some point?

 

Guys, where did you find, that rear O2 sensor has anything to do with poor fuel economy? As far as I know, it only checks the catalitic condition.

 

You were getting 32MPG on the highway DAMN!!!! are you sure something is wrong? i get 22-24 mpg and that is about 360-380 miles on a full tank. i fill her up reset the trip and once the light comes on its anywhere inbetween that. Personally i don't think there is anything wrong with your car, also your 5speed and i am sure you drive a little agressive and depending on where you shift it could just be you. 22mpg isn't that bad but i would just wait until the )2 sensors die if i were you.

 

my check engine light went on...ECU gave out o2 sensor codes....gas mileage is down about 80-100 miles a tank

 

When the rear O2 isn't working properly it throws the car into safe mode. This makes it run extremely rich. Thus reducing power and fuel economy. This is very clear with an OBD-II reader. Last time mine was bad I looked up the values. It was reading zero volts consistantly meaning it was totally dead. While reading that I looked up the short term fuel trim. The flow on the fuel system was way up there in comparison to normal idle flow rates.
More info and people agreeing with me in this thread:
http://forums.maxima.org/showthread.php?t=364724

 

Does a clogged fuel filter decrease fuel economy ?!? General thinking is that a clogged filter only lets les gas into the injectors and hence shud technically reduce the performance and not the fuel economy. Someone tell me this is wrong!!!

 

well, believe it or not, i think it was my tire pressure!
i just went on another trip today, and before the return trip, so halfway through the trip, i checked the tire pressure, and it was about 23.5! and that was when they were hot! so i put them at about 31, and i ended up with 28 or so mpg. i think that if they were the proper pressure the whole trip, i would be back to normal.

guess pressure really does affect your mpg!!

 

any effect of clogged fuel filter on fuel economy ?!?

 

31? I run mine at 44. I couldn't live on 31. Quite literally, I'd be dead.

 

that seems extremely high. what is the max pressure for your tires?

 

44... That is there primarily as a liability issue. Tires can take much more pressure than is listed on the sidewall. I run my rears at 50 on the 1/4.