Ultra Gauge Runs with Key Off
 

I noticed my Ultra Gauge reads .08 GPH with key on engine off. What exactly is it calculating to come up with that number? I've had it drop my average a little if I'm messing with it for too long. Anybody else have this issue? It's a
'99 Saturn SL2.

mine goes blank when i turn it to engine off, if i then turn it back to ignition on it turns back on but shows either "0.00 MPG" or "err"

I should have put "engine off". A little confusing, but you get the idea.

Do any other sensors read higher than they should at that time like TPS?

Nope. TPS @ 0%. Nothing else that I've seen. Just noticed that my avg mpg will drop a tenth or two if I sit too long with the key on. It seems to have dropped to .06 GPH from .08 after I did the mileage calibration.

It's probably residual voltage bleeding through, specific to your car. Some, for instance, don't close their TPS completely. My wife's Hyundai Elantra keeps something on with the ignition on/engine off, so its avg mpg (as indicated by Scangauge) keeps on declining with ignition on/engine off.