I have an 05 mini s with 145k on it. I have been monitoring my gas milage for a few weeks now and it has dropped to 22-23 mpg. I drive 99% highway, and I have need driving easy to make sure it just wasn't me playing. I have tried fuel injector cleaner and nothing. As far as I know the fuel injectors are original. I do have an o2 sensor that needs replaced, but I don't think that would drop my mpg that much.

Any ideas here would be great I need to get this fixed asap, I drive around 50 miles a day.

 

Replace the O2 sensor and report back. If you have a CEL for the O2 sensor, the engine is essentially running "open loop" or limp home mode which is going to be rich to protect the internal components.

 

Ah ok, do you know if both of them are the same part number?

 

They are the same: 11780872674

On a similar note, I get pretty bad mileage as well. Not as bad as you, but I drove just about 100% highway one time without ever pushing it and I got 26mpg. Around town I have always gotten 20-21. This isn't normal is it? Aren't 6MT R53's rated for 25/34?

 

they are rated 29 hwy, I can usually get 31 at 70 mph. O2 sensor and airfiler are huge impacts to fuel mileage. clogged injectors will get you better on the highway, since there will be less fuel in the motor. which is bad. but a bad 02 will either give bad readings or make the car run high fuel trim, which runs richer for protection. unless your doing 85-90 on the highway, then yes very possible for 25 mpg or worse

 

If your bypass valve is stuck shut, you'll lose about 10% fuel mileage.

 

Depending on where you live, the colder weather will also drop your MPG and the gas during the winter (winterblend) can also cause it to drop. Yes, replace the sensor that is an issue. Have it HERE if needed.

 

Helix where is the bypass valve at?

 

It's underneath the right side of the intercooler. You can actuate it manually by pushing on that tab that's resting on the stud in the foreground of this pic:

 

Here it is on the diagram. #22 below.

 

^Yep, if you open your hood, look for the S emblem on the plastic intercooler cover (the radiator on the top of your motor). Below that is a 'bullhorn' shaped intake. Follow that down and peer below it. You'll see the above pictured item. Have an assistant sit in the car as you look at the black plastic arm that attaches to the plastic round bit. Ask your assistant to rev the motor (in neutral) pretty aggressively and then let it idle. That arm should move. If it doesn't that could be your culprit.

 

I get about 22/23 mpg driving around here in hawaii.. we have plenty of stop and go traffic on our freeway.

 

in NH could get 27-29..., about 70-90 highway, cruise on with the speed set to 72 MPG..about 3200 rpm if I recall was the best rpm..higher rpme was a drop in MPG...with 16 or 15 inch rims...195 width....did better with the lighter 15's...wide tires can add rolling resistance...and heavy rims, like s-lites, can kill MPG.

 

Do you have a part number and price?

 

I guess that explains my poor MPG. I'm on 17" S-lites at 205/45...

Part number 11617568423, $111.23 from ECS, here.

 

Yes, it is HERE. Let me know if you have any questions.

 

Thanks for the post looks like Sevin has it there.

 

Bypass valve is working, picking up o2 sensor now. Do I need to clear the service engine light or will it go off automatically?

 

Clear it.

 

It may turn off on its own, but the code will still be stored so make sure to go in and clear it to avoid it being present if the CEL comes back on in the future for something unrelated.

 

I would get about 26 driving in the city and up to 31 highway. It's dropped about 2mpg, and I have a DT bypass valve. I know I can get better, but have the nightmare P2096 with a Milltek H/E.