^if you have a bov you need to do the dual setup or relocate the maf otherwise you will keep having idle problems, try this before coming to a stop press one time on the gas pedal lightly that may help keep you from stalling or having the rpms dip to 0 and bounce back to 1.
the cars run rich from the factory but you shold be getting better gas mileage than what you are, did you seafoam the car? if not this is what you do:
go to advance auto and buy two cans of seafoam (not seafoam deep creep, these are two different products)
with a friend in the car take the hose off the pcv (while car is running) your firend will have to keep giving the car gas because it will want to die) slowly with the funnel over the hose pour in 1/3 or about 5 oz of seafoam in the line (your friend will have to keep revving the engine to keep it from dying and you will see a lot of white s*** come out of your exhaust pipe this is normal) after pouring in the 1/3 or 5 oz turn the car off for five minutes) recconect the hose to the pcv and start the car, drive around for twenty minutes.
to help clean the fuel injectors which may help with the gas mileage pour one ounce of seafoam per gallon of gas currently in your car into the gas tank (if car is full (14 gallons pour in 14 oz of seafoam) drive until gas light comes on and fill up with gas like normal.
also before your next oil change (approx 100 miles before) pour 1/3 of can of seafoam into engine oil to help clean out carbon builup (pouring into the pcv cleans upper cylinder heads, putting in oil helps clean everything else oil touches)(both help remove carbon deposits)
this may help with your mpg problems. you may also want to check your fuel filter. if this stuff doesnt help i am out of ideas