2006 ford 500 fwd 140k miles yellow wrench light came on? Sorry so long?

I took over the payments on this car about 3 months ago when I first drove it I noticed when at a idle the engine would rev up and back down in any gear it would only do it 1 or twice a week didn't think much of it there was no check engine light about a month later engine light came on car still same just reved sometimes was going to go get it scanned but the next day light was off so though ok not going to worry its running fine drove for 2 weeks or so light would come on and off sometime s fast forward to 3 days ago… I go to work in car come out work battery dead hmm so thought maybe I left light on or something so got a jump from my boss started it up drove home 35 miles figured alternator would charge it up get home kill it and recrank starts fine kill it come back out 30 min battery dead so figured bad cell put new battery in everything good battery not dying so go to work next day and on the way its starts to die everytime I come to stop crank it back give a little gas ease into drive then it runs smooth while driving get to work 8 hrs get out car runs perfect never dies engine light off s today go to work its dying sat every stop engine light comes on go home still dying get close to home YELlow wrench light comes on car start jerking when leaving from a stop… Clears up runs ok kill car wrench light goes away drive comes back after awhile… Any thoughts on what's happening and what the yellow wrench light means thanks… Not Fuel filter/pump

Go to auto parts store that advertises "free code check/scan" Get it done, and write down all codes. Buy repair manual for this car (Chilton's, Hanes, etc., $25.00) Look up codes and troubleshoot tips. Go from there. Clean Mass Airflow Sensor, change spark plugs, wires, distributor cap and rotor (if applicable) Yellow wrench is a "service engine soon" indicator.