2003 Focus Rough Idle on Cold Start

I have a 2003 Focus with 79k miles on it. I notice that it idles rough om a cold start and continues for a few miles down the road. Then it smoths out. The engine seems fine and also the the transmission. I have check all the fluids and they are fine. I did notice the air filter is dirty and needs changing. I haven't changed it yet though. i will get it changed tomorrow, but didn't think it could cause a rough idle.

Anyone have any ideas as what the cause may be?

What engine do you have 2.0 ztec,2.0 SPI or a 2.3 , is there a check engine soon light on? If there is any more information you could give me would be helpful in the proper diagnosis.

I know its a 2.0L and no check engine light is on.

It's a 2.0L split port engine.

My best guess would be to check for vacuum leaks. After it warms up does it still Idle rough or smooth? When the engine is cold it needs more fuel to run properly so the computer goes in to a "fuel enrichment" mode if you have any vacuum leaks they could be starving the engine when cold. Just an idea, hard to say exactly with out hooking it up to a computer and watching the engine PIDS "Parameter Identification Data"