So, when the engine sounds like it is going to die on you after pulling carb heat on, don't immediately go to back to cold power - keep carb heat on while turning towards a suitable field, just in case.
biscuit74,
This is the first time (that I can remember) that I have seen this aspect of carb icing mentioned.
I had been flying for about six years (~500 hours) before I experienced carb icing. I was flying a 172 in the summer time, about 4000' AGL near the Canadian Rockies, with cloud base not much higher (i.e. about 4000' lower than normal), with virga coming out of most of the clouds. Passing near one of these clouds, I thought it would be prudent to check for icing. I pulled on the carb heat and got the symptoms you described. The point of this long-winded preamble is that it scared me so much that I instinctively put the carb heat back to cold!
It was only after thinking about it for a minute that I realized what was happening and put the carb heat on again and let the engine cough and splutter as the ice melted.
I wish one of my instructors had mentioned this issue during my training. Not one ever did.