So, my 2006 tC just hit 60k miles. Over the last few months I've noticed that I'm averaging 23/24 mpg. Before these last few months I was averaging 28/29 mpg. I've also started getting a slight rough idle (jumping between 500 and 700 rpms).

I haven't changed my driving habits or route in the last 3 years, so I'm fairly certain that neither of those factors should be affecting this recent change.

Everything on the car is stock, It's a manual, and fairly certain I've done all the maintenance up to this point with the exception of changing the tranny fluid (will be doing that real soon since I just hit the mark for it). I've replaced the sparkplugs (stock iridium for ngk iridium), even though they still looked fine. the air filter looks fine as well.

I'm kinda thinking that I should clean my MAF, just in case but it's a bit expensive still for me to mess with it if it wouldn't really be related.

Does anyone have suggestions for things to check that could be causing this?

 

I heard its the new blend/mixtures of the gas. I use to get about 320 miles a tank and now I can barely get 280 miles.

 

I read an article that claimed gas mileage is at its worst during the middle of your car's life. You get good mileage when it's new, then it drops off, then climbs back up to what was on the sticker as the mileage increases. It seems to be holding true for me at least. I got 400 miles out of my last tank and I'm nearing 100k miles.

 

yeah krazy, that's pretty close to the same as where I am.

Though, if I put in pretty much any sort of gas additive it climbs back up. So perhaps it is something with the gas.

 

even though my 2010 only has about 15k miles, this topic is always an interest to me. I drive half city and half highway and get about 300 before the light comes on now and I fill 87 shell or chevron. when i first got the car, i can get 330 before the light hits.

gonna watch and see what others have to say.

 

Found this: http://blog.gasbuddy.com/posts/Winte...22955-413.aspx

Article doesn't metion anything about ethanol tho. Just found out that gas stations aren't required by law to mention anything about ethanol unless its over 10%...

 

Weird, my car is only 10k miles and never really made over 300miles a tank. Its IHE modded, and fed w/ Shell 89 gas. I have synthetic oil and drive like 70% city and 30% highway. Is the gas mileage normal, or its a bit low?

 

better stick with 87 I guess! I've always use 87 in my car for 4.5 years, and only only one time i did fill it with 89 or 91 doesn't feel any different so I stick with what the engineer are design our car for.

28/29 mpg that's impposible!!! when the car is only (cty/hwy): 20/27 mpg unless your 06 has a smaller engine then my 07!

I always though that my mpg is dropping, since everytime I pump my gas I see it's around 300-320miles so i'm sitting at 25mpg for 45% city 45% hwy, plus 10% aggressive driving some time. so I think i'm still in the good shape, also I have 07 with 60k only did oil change at ever 3.5k, tranny fluid and seafoam at 55k.

 

my car does the rough idle every once in a while as well (07 with 56k on it) and my gas milage has dropped off. Glad to see im not the only one.

 

you're in the same situation as I do now rough idle, I'm gonna try to clean my MAF sensor, seafoam and swap out the spark plugs today after work. Hope that get my baby back to the day one.

 

Ya, after this weekend i might try some new plugs and see where that gets me

 

you do realize, fuel filter should never need to be changed. Nor should you need to do a fuel injector cleaning. Toyota says that this should last a lifetime. Loss of fuel mileage is due to the change in gasoline. I checked myself w/ my personal service advisor about the same issue I now noticed w/ my car. He said no worries, you dont need a cleaning, a fuel filter replacement or anything along that line..

 

Don't know where you're located, but gasoline is usually switched to a different formula which is less prone to freezing in the cold winter months. It does have detrimental effects on mpg. Very common here in the Northeast.

If you're in a warmer climate - even colder temps in the am/pm during fall/winter with "summer" fuel can effect mpg slightly, because dense colder air makes more power, which also hurts mpg.

It is possible to beat the old govt mpg ratings; in 06 they were using the old system, which didn't have the ac on, and left electronic controls off. Also the top speed tested on the highway was 55. When was the last time you went 55 on the hwy, lol.