On My 1991 Corsica 3.1 V6 Engine Starts To Miss After Engine Warms To Oper Temp The Check Eng Lite Dose Not Stay On Only Blinks When When Missing It Dose Not Do All The Timebut The More I Drive The Worse It Becomes .stalls In Town But Starts Right Back Up .have Replaced Plug &wires Coil Packs (3) Ingnition Module O2 Sensor Coolent Sensor Also.had To A Chevy Dealer They Found No Stored Codes.any Help Is Greatly Needed Thank You

Could be a vacuum leak or an injector. Did you isolate which cylinder is misfiring?