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,

1 answer
Have a COMPETENT shop check it...