While fixing a vacuum line affecting my A/C yesterday, I noticed another vacuum line that had been plugged (and plugged crudely, at that). After looking around some, and referring to the vacuum diagram, I determined that it originally went to my vapor canister. I looked at the canister and it appears that however the line was connected is no longer there, and someone just plugged the line for a quick fix. Could this have any affect on my fuel mileage? The way I understand it, without the vacuum line fuel vapor would just leak right out into the engine bay, but how much vapor really comes out of there?

 

Depends on temperature, barometric pressure, slosh, type of fuel (summer blend/winter blend/CARFG/etc.), level in the tank... No; not much comes out, and it won't have a noticeable impact on economy.

 

So it's not something I should rush out and fix right away, then?

 

It's certainly not HELPING anything... At best, it's hiding the real problem.