As an operator of 4 PA28's you will find that the only solution is to change the left mag which is probably giving a week spark at low temperatures.
I have had to change the left mag on a different a/c on each of the last two winters,and am waiting
for the spares suppliers to open again after the new year to order another left mag for another of the Cherokee's.
However, before going to this expensive option do get the primer system injectors checked for blockages,I have all our injectors cleaned every year but admittedly the a/c are achieving a lot of hours each year.
regards