1999 Ford Taurus Stalling out at lights

Engine Performance problem
1999 Ford Taurus Front Wheel Drive Automatic 190000 miles

I have codes P171, 174, and 1744. Around inspection time, I discovered that keeping the overdrive switched off keeps all of these codes away and the check engine light will not come on. The car has driven fine with these codes on for almost a year, but recently began stalling out at lights. My mechanic suspects a vacuum leak due to the 171 and 174 codes. But now I'm wondering if these codes might be a red herring: since keeping overdrive off avoided the 171 and 174 codes, I'm thinking they must be somehow connected to the 1744. Also, these codes have been on for a long time and the stalling trouble is recent. Thank you for any input you can offer.