Last year I got a valve adjustment from a friend (an Acura tech) on my B18C. He did it as soon as pulled into his driveway, not allowing the engine to cool down. I said something about it and he kinda brushed it off like it was nothing.

Well, as soon as I got it done, the valves were quiet but there seemed to be a misfire when it warmed up. Now after sitting all winter, it seems to be even worse, but still no noise from the head at all. It only does it at idle, and the car seems to performing well.

Would a bad valve adjustment cause the misfiring?

 

No, but your lash could of been adjusted too tight. Have someone (or you) check the lash when the engine is cold (like in the morning before you drive) and make sure they're within spec.