HafPint

Hey Forum, I'm a Newbee, and I just notice that my MPG Display is fluctuating all over the place from 5mpg to 80mpg (up & down all over the place). I just got it out of the shop and right away noticed that my mileage trip had been reset, the mechanic simply pressed the button to reset the mileage, but as I'm driving the mpg display is going up and down, never seen this before, any thoughts?

Thanks

HafPint

mmarshall

Welcome to CL as a new poster.

In most cases, there is a fairly simple explanation to your Yo-Yo MPG readings. Right after the trip odometer has been reset, particularly if you have just gassed up, the trip-computer will constantly compare the instant-MPG of the engine, based on fuel-flow, against the total mileage accumulated since the reset...which, for the first few miles after the reset, is close to zero in the single-digits. As you accelerate from a stop or at low speeds, you use a lot more gas.....and the accumulated MPG, based on the low miles traveled, is very low. Letting up on the gas will, correspondingly, give very high readings....perhaps up to 99 MPG. This yo-yo effect will be strong and pronounced for the first few miles, but gradually get more even and stable as the accumulated miles accumulate since the last fillup and/or reset. That is because the computer is then comparing the instant and accumulated MPG against a greater number of miles travelled, which gives you a more stable ratio. This behavior is normal, and every vehicle I have owned with an electronic trip-computer has behaved in the same way.

HafPint

Thanks for your reply MMarshall, I just had new Motor Mounts replaced, I was worried that the fluctuation was a result of the replacements. I have read from the forum that their is a reset button on the left side of the steering, do you think this will regulate the proper mpg if I use it? Also, would you use Fuel Injector Cleaner for better fuel mileage?

Thanks again for Replying....

HafPint

mmarshall

Use a good Tier-1 fuel brand of gas with good detergent-additive packages (the two best brands are arguably Shell and Chevron) and you probably won't have to use a separate fuel-system cleaner later on.....the additive package in the gas will probably do that for you. But Shell and Chevron are not the only good Tier-1 Brands...there are a number of them. What you generally want to avoid is the cheap Mom-and-Pop stations...that gas is cheaper for a reason, and often skimps on the additives, so your engine builds up carbon.

Keep an eye on the trip-computer and the Instant-MPG and accumulated-MPG readouts. In normal operation, the Instant-MPG will keep fluctuating up and down quickly as you press on and let up on the gas pedal, because it is based on instant engine-response. That will NOT change as miles build up. But the Accumulated-MPG figure WILL stabilize and react more slowly as time and miles build up. If it doesn't do that and stabilize with time, then you may (?) have a problem with the trip-computer itself or the electronics/software that operates it. That part goes beyond my knowledge, and you would need a technician or a new trip-computer display.

HafPint

Oooohboy Pray its doesn't have any computer glitches. Thanks for the feedback and if there are other Lexus Mind Bogglers out there that may have or has had a similar issue, please feel free to share.

HafPint