Tries starting itself with dash lighting up and lights flickering, now constant misfires.

I've had purge valve replaced, oil sensor, regular oil
changes, buy gas at same place but have a
constant misfire at stoplights or even just driving I
can feel it jump. It smells like exhaust fumes in the
car, my heat doesn't always work and out of 4
repair shops noone can seem to find the problem.
Getting frustrated please help.