Decreased MPG

[ellroy2]

Been checking out this board ever since I bought our '08 4Runner, but have not posted until now. A lot of good info on this site.

I have recently noticed that our 4Runner is not getting as good as MPG as it always has. We have had it for almost 4.5 years(64K on it) and have never had any big fluctuations in gas mileage that I have noticed. I don't watch it like a hawk usually, but I do pay attention to the mileage range on the little trip computer thing. It has always ranged from 390 to 415 after fillup. Average MPG on the trip computer has always been in the 19-21 range.

A couple months back, I noticed that the range was only getting up to 380-385 after fillup. Now all of a sudden it has dropped to 360 on the last fillup. I just reset the MPG and after driving about 20 miles(5 on the highway) it says I am only getting 15 MPG. I have never seen it that low, even with just city driving. Both me and my wife are pretty light to normal drivers. So it seems that the vehicle is getting 2 or 3 less MPG, or 40+ less miles per tank. That concerns me since we have not changed driving habits compared to the last 4 years.

So any suggestions on where to begin? I know it could be a lot of different things. Tires are to pressure and air filter should be clean(K&N). At 60K(3 months ago), I replaced the spark plugs and changed the front and rear differential and transfer case oil myself. Tires are a couple years old with $20k on them(Michelin LTX M/S2). Some people talk about winter blend gasoline, but I don't know if the stations in the city switched to that and how much of a difference that really makes. It has been cold this winter, but not lower than 15 or 20 degrees at night. I have never noticed a big difference in MPG in the winter. I also hear people talk about the O2 sensors and the MAF. How do you check to know if the O2 sensor is bad? Also I am worried that maybe the spark plugs I put in are bad or something. I used Denso plugs and made sure they were gapped correctly. I did them myself at 30k as well and didn't notice anything back then. Could the spark plug wires cause a decrease in MPG, and how do you check for that? Any other suggestions?

I hate spending extra money on gas!

 

[LTDSC]

you have coil packs, not wires. I would just bet its winter gas blend and or driving conditions. Seems like you've done everything else to help the cause.

 

[aha2988]

Been checking out this board ever since I bought our '08 4Runner, but have not posted until now. A lot of good info on this site.

I have recently noticed that our 4Runner is not getting as good as MPG as it always has. We have had it for almost 4.5 years(64K on it) and have never had any big fluctuations in gas mileage that I have noticed. I don't watch it like a hawk usually, but I do pay attention to the mileage range on the little trip computer thing. It has always ranged from 390 to 415 after fillup. Average MPG on the trip computer has always been in the 19-21 range.

A couple months back, I noticed that the range was only getting up to 380-385 after fillup. Now all of a sudden it has dropped to 360 on the last fillup. I just reset the MPG and after driving about 20 miles(5 on the highway) it says I am only getting 15 MPG. I have never seen it that low, even with just city driving. Both me and my wife are pretty light to normal drivers. So it seems that the vehicle is getting 2 or 3 less MPG, or 40+ less miles per tank. That concerns me since we have not changed driving habits compared to the last 4 years.

So any suggestions on where to begin? I know it could be a lot of different things. Tires are to pressure and air filter should be clean(K&N). At 60K(3 months ago), I replaced the spark plugs and changed the front and rear differential and transfer case oil myself. Tires are a couple years old with $20k on them(Michelin LTX M/S2). Some people talk about winter blend gasoline, but I don't know if the stations in the city switched to that and how much of a difference that really makes. It has been cold this winter, but not lower than 15 or 20 degrees at night. I have never noticed a big difference in MPG in the winter. I also hear people talk about the O2 sensors and the MAF. How do you check to know if the O2 sensor is bad? Also I am worried that maybe the spark plugs I put in are bad or something. I used Denso plugs and made sure they were gapped correctly. I did them myself at 30k as well and didn't notice anything back then. Could the spark plug wires cause a decrease in MPG, and how do you check for that? Any other suggestions?

I hate spending extra money on gas!

over time gunk and debris build up in the throttle body. when your truck is idling the throttle body butterfly valve is closed; however, a small gap is still open at the top and bottom to allow just enough air to pass through the intake to maintain air/fuel mixture at idle. As the gunk builds up the gap closes so when idling you begin to burn less and less air and more gas to keep the rpm's at the idle range. The mas air flow sensor being dirty can also cause and mpg decrease effect in the sense that if it doesn't know how much air is going into the engine the ECU can't properly mix the correct air/fuel mix to maintain the most efficient mixture.

suggestions would be to remove and clean your throttle body with throttle body cleaner (you don't have to remove it but it's a lot easier to work with off the truck to really clean the gunk off)

and clean your MAF sensor with MAF sensor cleaner.

If you are feeling a drag or an increase in rolling resistance you could possibly have a seized caliper. to check for this you can simply jack the vehicle up getting all 4 tires off the ground in neutral spin each tire by hand to ensure they all have equal resistance. if one is harder to turn than the other you have found a seized caliper piston.

hope one of these items helps

 

[ellroy2]

suggestions would be to remove and clean your throttle body with throttle body cleaner (you don't have to remove it but it's a lot easier to work with off the truck to really clean the gunk off)

and clean your MAF sensor with MAF sensor cleaner.

Does anyone have detailed instructions/photos of how to clean the throttle body and MAF sensor? Can you buy the two cleaners at any auto parts store? I am not the most mechanically smart person, but I usually can figure things out with a little instruction. Thanks

 

[aha2988]

Does anyone have detailed instructions/photos of how to clean the throttle body and MAF sensor? Can you buy the two cleaners at any auto parts store? I am not the most mechanically smart person, but I usually can figure things out with a little instruction. Thanks

you can get both the cleaners at the local auto parts stores

there brand name is CRC you'll need a can or two of "throttle body cleaner" and one can of "MAF sensor cleaner". They tittle the cans that way to you can't miss them. or just ask one of the sales people to help you. Once you get the cleaners shoot me a PM I'll give you the details on how to get it done. Its easy work for sure!

 

[lehiguy]

I went on a little quest today, removing the airbox, inspecting the throttle body, etc. I found something I couldn't identify, a type of filter or difuser behind the air filter. It looked dirty and restrictive, so I removed it although the design indicates that it is intended to be permanent. Come to find out, it is some type of fuel vapor trap. I am curious to see if my mileage improves.