I start my 2001 sable below 50 degrees it violently shakes jumps stalls whats up on 2001 Mercury Sable

repair shop has diff answers every visit to much $ spent , otherwise perfect in the warmer months, no issues not dependable now what is the issue, 1st needed plugs, done, back fired once, ?o2 sensors then ok,

Asked by for the 2001 Mercury Sable
Have a COMPETENT shop check it...