Gas Milage fluctuating

[JDMMA70]

Is this normal also i think i have a vacuum leak somewhere and i hear something hissing on the turbo side of the engine. When my dad and i replaced my fan clutch this morning i drove it around to see if my milage improved. It did it went up to 15.2mpg but when everytime i came to a stop light the mpg would start dropping down to to close to 13mpg. Also when its idling its rought (my guess is vacuum leak)

Car is Automatic

Thanks
~JDMMA70

 

[Rennat]

idling doesnt help MPG. your using fuel and going no where... so its essiantly 0 MPG.

and if you "think" you have a vaccum leak, then start zip tieing all of your lines.