My '73 182 with an O-470R requires some (sometimes full) carb heat to get a good mag check at cold temps. I find it the norm below about 10 F. No problems at warmer temps. During the summer I keep the mixture leaned as far as it will idle smoothly while on the ground, keeps the rough mag check away.

Recently we had a problem with the 180 (135 bird). Turned out both mags were sick, one was toast and the other was ready to give up the ghost too. It just wouldn't start one day after coming in from a flight only an hour before. The only symptoms were hard starting, we thought we were flooding it (after 800 hours of trouble free operation). No bad Mag drops on run-up, it just wouldn't start again. Replaced both mags, problem gone.

weather has been so bad around here have not had chance to do any flying, i.e. have not had the chance to start plane and do run-up. will report results when sun comes out.

Mechanics work even in bad weather. I can't imagine why you wouldn't talk to your mechanic about this, and have them take a look. I seriously doubt it's going to fix itself. And, if you have that large a mag drop the airplane is not airworthy.

MTV