[filmfolks]

Hello all, long time lurker and learner here. My 5th Bimmer in 25 years.

bought a new to me 2015 328 XDrive touring, and mmmmm it has the M Package and red seats.
Pretty happy, BUT the gas mileage has been abysmal. So, Im cleaning and have replaced sensors for efi. Thats made some definite improvement but the idle appears to uses lot of gas, turning on the AC at idle makes the car very unhappy so im trying to trouble shoot.

here's what I don't know as I get to know the car and the dum question.

On the Efficient Dynamics display at idle its saying im getting the lowest "mileage" , Ie using the most gas over a span of time. shows highway at 33-40 etc, town average 22 sih. But at idle it all the way down. Is this normal?

I fully understand how the MPG Guess-O-Mometer the cars use to get flawed consumption info and (Ive had a lot of cars) I calculate MPG on fill up. My last wagon 27 mpg solid every time- 25 2g= new plugs/air filter.
But i had a thing where this car idled in the parking lot for 60 min and used 1/8 of a tank or better. After some tweaks and sensors, 28 mpg on a 300 mile stop and go traffic highway trip. 16 or less around town.

So is the idle MPG thing on the display normal, I hope to use the info to track down the issue.

thanks
J

[Orion4]

At idle, you are getting 0mpg! Therefore drives you avg. MPG down quickly (depending how recently you reset it). So yes, that correct!

[tturedraider]

Originally Posted by Orion4

At idle, you are getting 0mpg! Therefore drives you avg. MPG down quickly (depending how recently you reset it). So yes, that correct!

This is correct. At idle the mpg indicator goes to zero.

[328dabi]

Idle = 0 miles per gallon as you are not moving so you are physically not covering any miles per gallon of fuel consumed.

[filmfolks]

Originally Posted by 328dabi

Idle = 0 miles per gallon as you are not moving so you are physically not covering any miles per gallon of fuel consumed.

Originally Posted by Orion4

At idle, you are getting 0mpg! Therefore drives you avg. MPG down quickly (depending how recently you reset it). So yes, that correct!

Originally Posted by 328dabi

Idle = 0 miles per gallon as you are not moving so you are physically not covering any miles per gallon of fuel consumed.

sorry if I wasnt clear.
the mpg is going DOWN not up on the bar. also lowering the "average" on the guess o mometer". IE coasting or stopping and the enginge stops, the indicator bar goes UP to 40 50 65MPG or HIGHER. at idle the mpg indicator goes DOWN to 10-12 mpg as if i was flooring it. After about ten tanks of gas now, pure higway is 26-28mp and confirms on a fill up. idling while working and scanning with short around town drives is 16-18 mpg also confirms on fill-ups.

[328dabi]

Coasting I get 99mpg(the highest it can read). At idle, 0

[Boznien]

Originally Posted by filmfolks

On the Efficient Dynamics display at idle its saying im getting the lowest "mileage" , Ie using the most gas over a span of time. shows highway at 33-40 etc, town average 22 sih. But at idle it all the way down. Is this normal?
J

MPG numbers are accurate.

As others said, idle is always 0 mpg because you're not moving anywhere haha.

(also, no such thing as a dumb question if the car is new to you.)

[filmfolks]

Originally Posted by Boznien

MPG numbers are accurate.

As others said, idle is always 0 mpg because you're not moving anywhere haha.

(also, no such thing as a dumb question if the car is new to you.)

at idle it says 12mpg

[filmfolks]

Originally Posted by Boznien

MPG numbers are accurate.

As others said, idle is always 0 mpg because you're not moving anywhere haha.

(also, no such thing as a dumb question if the car is new to you.)

its not zero. its 12.(Eco meter is in thirds) at idle it used well over an 1/8 of a tank in an hour. that's two gallons of fuel. at highway speeds thats around around 60 miles worth of fuel. (28-30+MPG)

the fuel trim driving its adding a couple points, at idle live data doesn't show a huge dump to the trim.

so the question im working on turns to why do i get better gas efficiency at 80mpg than at idle.

My dumb question(thanks for understanding) is why does the meter says 12 mpg at idle and not zero or close to it, like when the car coasts (the blue bar all the way up in the efficent dynamics display)and has anybody looked at that and these cars just eat gas at idle.

[Wires]

Originally Posted by filmfolks

My dumb question(thanks for understanding) is why does the meter says 12 mpg at idle and not zero or close to it, like when the car coasts (the blue bar all the way up in the efficent dynamics display)and has anybody looked at that and these cars just eat gas at idle.

I think you are confused at what you are seeing. The MPG gauge calculates what the MPG is based on the amount of fuel going into the engine vs miles travelled. It's not a "guess 'o meter", it 100% knows down to a microsecond on how much fuel was dispersed at any time.

The only "fudge" part of that is if you do brief hard acceleration, then it ignores that from the displayed MPG since that's not a consistent consumption value.

If you are idling, and the MPG gauge hasn't been reset forever, it will slowly average the number down over time. If you reset it, then you should see it basically be 0 MPG when idling.

And, EVERY car eats gas at idle. You aren't driving, engine is running, do you expect that to be free?

[eff32fl]

Originally Posted by Wires

I think you are confused at what you are seeing. The MPG gauge calculates what the MPG is based on the amount of fuel going into the engine vs miles travelled. It's not a "guess 'o meter", it 100% knows down to a microsecond on how much fuel was dispersed at any time.

The only "fudge" part of that is if you do brief hard acceleration, then it ignores that from the displayed MPG since that's not a consistent consumption value.

If you are idling, and the MPG gauge hasn't been reset forever, it will slowly average the number down over time. If you reset it, then you should see it basically be 0 MPG when idling.

And, EVERY car eats gas at idle. You aren't driving, engine is running, do you expect that to be free?

This is partly why auto start/stop exists, to avoid unnecessary emissions and to save gas. Getting 0 MPG while idling for a while is a waste of gas.

[filmfolks]

Thanks all.
its NOT reading zero, its reading 12 at idle. so not normal. too much fuel is being added.
long fuel trim is adding 8-9%, sometimes. better after warm up. even better after on second drive after warm up.
slight lean code indicated, sometimes.
rough idle, slightly high engine vacuum . ordered new Cvv(pcv)
battery runs down when not charging or running to 11.9 and takes a few moments to return to full charging. still starts. new battery pick up at bmw tomorrow.