C-182 carb-heat causing rough running.

It's normal. I don't use carb heat because it's not needed where I
live. Don't use carb heat in the pattern just because the checklist
calls for it. Use it when you need it.

AOPA sez carb ice can be encountered at inlet air temps up to 104
degF. They also have a chart that they occasionally publish that
shows the tendency to generate carb ice as a function of inlet air
temp & relative humidity. This chart shows a real coffin corner at
high humidities around 50 deg F. Higher temps and there will be less
tendency of course, and at lower temps there isn't necessarily enough
moisture in the air to form ice.

That chart should be posted more widely. I can't find it just now,
but it was recently on their web site. It should be necessary
studying for us flying with carburetors.