So I went out to my 95 850 turbo today and the battery was almost dead. Motor would not turn over enough to start.
So I charged batt. for a while and it started up just fine.
I left it idling for about 20 min. to close up shop.
Then turned it off and started it back up just to be sure it would work. I'm going to get a batt. tomorrow since this one is a few years old.
Well, after I drove a few hundred yards and looked down at the MPG, MPH, Avg. MPG, Temp etc. computer, I noticed it was reading backwards on the avg. MPG. I would accell and the MPG would go DOWN. The coast and I would get 1 MPG. Then when I checked the other options it was the same weirdness. My avg. speed was going up by the second (above 80) even though I was doing about 30.
I reset everything but it is doing the same thing.
I already turned the car off and on a few times. Its the same.

I also did a search and didn't see anything like this.

Is there anything I need to do to fix this? I'm kinda confused.

TIA

 

Did you try resetting the ECU?

I would just get that new battery and see if that helps.

When you go to take the battery out of it currently, hit the brake pedal ten times just to make sure there isn't any juice flowing still (its possible).

Let that be for about a half hour and put the new battery in. MIGHT clear your problem.

 

Get a new battery and reset the ECU, It should help