gas has to flow from the engine to the sensor, that takes some amount of time. The ratio should be correct, but the time it's recorded is more delayed from when it happened.
Later
"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut." - Albert Einstein
When was the last time you *really* did something with your Z to call yourself a Z enthusiast?