MPG indicator fluctuates, steering turns on its own, weird smell

Fuel economy indicator is just that, an indicator, it works on a flow and demand. When idling low flow and low demand, driving, these may be on a Honda a vacuum gauge type reading, same thing idle is high vacuum/low fuel requirement drive open throttle low vacuum higher fuel usage. Get the alignment and steering/suspension and tires check for any problem. This is the most common cause of steering wander. The smell can be anything, it can be something stuck on the exhaust and smelling when hot. Get this looked at first.