There are the 3 lines coming form the back of the car to the front. 2 of them are for fuel. The third which looks like a vacuum line. How important is that "vacuum line" and what does it do? If anyone could help let me know Thanks Mike

 

It is the EVAP canister purge line from the engine to the charcoal canister in the LH rear wheel well.

 

Would it create a problem if it isn't hooked up?

 

It can allow an annoying gas smell. There would also be a vacuum leak to the engine, if the hose were laying unplugged.