I have a 2000 Audi A4. Since it has started to get cold I have noticed that my car has a tendency to idle rough at start and occasionally ( depending on the temperature) the check engine light will come on. This has only begun to happen since the temperature outside has dropped below 40 at night.
Prior to this problem(in the past month) I had all of my coil packs replaced, as well as my temp sensor and spark plugs.
most likely this is an air/fuel mixture issue, not an ignition problem. Have it checked for codes, even if there is not check engine light. Possible causes are crank or cam position sensor, or mass air flow control of some kind.