Rough Idle with Heat on

[Carchrism5]

I live in CT and it has been very cold, like 25 degrees this morning, and i have noticed in the morning when i go out and start the car up and turn the Heat/ Defroster on it doesn't idle smoothly, like it will go from 800RPMs to 1,100RPMs, it sounds like someone is pressing the gas repeatedly, i can hear it when i go inside. Has anyone had this problem or know how to fix it?
Thanks

[quicksilverdon]

I believe that's normal. When you put defrost on, it automatically turns on the A/C. The A/C, plus cold temp, tell computer to keep engine idle high. Leave the fan on 0 until it warms up a bit.

[tpscruiser]

QSD hit the nail on the head! Also when you turn on the Rear Window Defroster/Heated Mirrors and Heated Seats (if equipped), you load up the charging system and that can cause some roughness at idle.