Why is this happening?

[Nyyankees3511]

I cleaned by throttle body and put some super gas (used regular before) yesterday and it seems as if my car is not making the gas mileage as before what could be wrong?

[Somedude]

if your car requires regular, only add regular. Adding a higher octane does nothing but gives you bad gas milage.

[SPF 0]

I've had people swear that their mileage improves after an oil change. My guess is that their tires (post change) are now properly inflated.

Has anything else changed since you last checked your mileage?

[Nyyankees3511]

I didnt change anything except different octane gas, kandn filter and the throttle body cleaning.

[SPF 0]

How old is the previous mileage reading?

[Jon11582]

If you got a V6, might be the fact that its actually using that gas to push some more power now, instead of retarding your engine so it can take regular gas. Been gunning it lately?

Thats the only way that higher octane can lead to lower gas mileage - the gas itself is no more or less effiecent.

Since you cleaned the filter and TB, it could be that it can now take in the air to use the extra fuel now, but again, youd have to be revving alot to actually notice a difference in gas mileage.

Just cruising, none of these changes should offer worse gas mileage.

[StockSolara]

If you got a V6, might be the fact that its actually using that gas to push some more power now, instead of retarding your engine so it can take regular gas. Been gunning it lately?

Thats the only way that higher octane can lead to lower gas mileage - the gas itself is no more or less effiecent.

Since you cleaned the filter and TB, it could be that it can now take in the air to use the extra fuel now, but again, youd have to be revving alot to actually notice a difference in gas mileage.

Just cruising, none of these changes should offer worse gas mileage.

very good reasons bro. . . and also maybe you're having too much fun listening the airbox w/o a resonator. . . haha

[Nyyankees3511]

Thats possible, i got 80 miles since the full mark and right now its a lil higher than 3/4.

[ChargedSolara]

sounds normal. i used to get close to 400 on a tank.

[Jetfixer]

It's a total waste of money to use higher octane fuel than what is called for in any modern car. The sensors on the car determine how lean/rich to run the engine and how much advance is required on the timing to maximize the burn efficiency and to prevent knocking. The computer is calibrated for the recommended fuel. Using a higher or much lower fuel causes the sensors to go beyond their calibrated range. This is treated by the computer as a failure condition and it adjusts the engine accordingly, which is to say, it now defaults to a "limp-in" mode which will allow it to run, but at miserable performance as you have seen. Also, the K&N filter allows higher airflow. It takes awhile for the computer to adjust to it. Mine took a few start/run/stop cycles before it ran right again and I use the "drop-in" replacement K&N, not the CAK.

[SPF 0]

It's a total waste of money to use higher octane fuel than what is called for in any modern car.

One caveat I might add in to that truism is that while, for example, my '05 SLE <i>can</i> run on 87 octane (as per the manual), the full horsepower rating was done on 91+.

While it'll run just fine on the lower rated gas, you will lose HP.

NOTE: This is not applicable to every vehicle.

[Hefty]

Make sure you didn't put the air filter in backwards. Also, double check that nothing got disconnected from messing with the throttle body. Your computer maybe running in closed loop mode if it has detected a sensor offline and this will impact driveability. Otherwise, wait till you put a few tanks through and see if it stays the same.

[Nyyankees3511]

the flat side goes up right?

[methyl mike]

I have a 99 v6 with over 100k what octane should i be using? I tend to use 87.

[mshearon]

Using higher octane gas is like buying bigger tennis shoes to make you run faster.