on start up. I will start up the car and will throw a check engine light for cylinder 4 miss fire. The outside temp has been much colder than ever, and this is during startup. Bad plug or coil pack? No other codes, seems to drive perfect otherwise. I also haven't gone full throttle in over a month, just drive it. TIA

 

you answered yourself... so change it... all of them.. and inspect the coils...

 

could be a multitude of items.. as marski said.. coil packs and new plugs are the first steps!

does the ecu have a flash and what oil are you using?

 

First instinct Coil Pack if you had said on boost I'd have said firstly plugs . But on this occasion most likely coil pack . Change them all for the 997 items & change you plugs for good measure.

 

I had this too - changed coil packs and plugs without success. It turned out to be an injector.

As others have said, start with coil packs and plugs.

 

Today i woke up and it was nearly 70 degrees in Boston MA, No miss fire no CEL!! Car runs as it should. Matter of fact for the first time since beginning of september ( my tragic boost leak experience) i finally got on it, I went full throttle in 2nd till 6k and full throttle in 3rd till about 5k just to feel it out...Everything smooth!!