intermittent misfires

Car is a 1999 bmw 323i. Throws code p0170 fuel trim malfunction and a couple others which stupid me I forgot. They were misfire codes naturally and a second fuel related code. Which has been on for a few thousand miles before the misfires started. I'm going to put in a new fuel filter since its as far as I know the factory unit with 165000 miles. Car runs great one minute then it limps along. I put it on a blue tooth type scan tool and of course it ran great so timing Fuel ratio etc showed good. I did notice that when the problem comes up it is upon start up and will go away after 10 minutes or so. Ill post the other codes when I get them. Thanks Nick.

most likely a ruptured crankcase vent valve.
or any of many other vacuum leaks.

Check the rubber elbow between the MAF and intake for cracks.

I will be checking any and all suggestions when I get home from work. Thanks for all the suggestions. Keep em coming.

Got it home and checked the easiest first. Big gaping hole Ingram the last rubber intake boot before the engine. Right on the smaller tube after the y. Not surd if its the only problem but it definitely was one. Thanks.

Intake boots replaced. Car runs great. No mis or check engine light. Thanks a lot.

Good deal...glad you got it fixed.