Idling problems

My car has been bucking or surging for about a year now. Especially when I turn the heat or A/C on. It seems to be worse on colder days. I'll be at a stop light and it will start bucking with my rpm's shooting up just a hair. I've also noticed my lights dim as it bucks. It accelerates and runs fine. Like I said just when I'm at a stop light with foot on brake or in reverse it wants to buck a lot. It also will do it in park but not as bad. It's not showing any codes and my local mechanic didn't notice anything go figure. After the engine is good and hot and I've ran it a bit though it doesn't do it nearly as bad? I'm thinking maybe it's got carbon build up somewhere. I've tried seafoam with no luck. Getting a can of bg 44k here soon. Any advice or recommendations would be great. Thanks!