Engine idle rough

The air conditioner compressor puts a heavy load on an idling engine so it is going to have to work harder. If the engine is misfiring, you will notice it a lot easier at idle. The check engine light should be on too with a diagnostic fault code telling which cylinder is responsible.

You might also have a simple case of idle speed too low. That occurs after the battery was disconnected or run dead. To solve that, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.