Can Misfire be caused from bad ICV or Vacuum leak?

[m3BMW95]

I just got finishing replacing all of my exhaust valves and thank god the car starts, runs, and does not leak any oil. It does however idle rough, and I pulled the codes. P0300, and misfire on cylinder 5 and 6. It does not do it all the time though. It will idle fine for a second at about 700 rpm, drop down to 5 or 600, and then seems to miss. The car runs good other than at idle. I did notice however if I was in 3rd gear at about 2500 with a little load on the engine, it seemed to miss and jerk a little. That has me thinking it is not the ICV, but I really can't feel it miss any other time, and it has the same power it used to. If the valve timing was off, would it cause this? Thanks

[HBpredhunter]

did you lap the valves and make sure they seated correctly...
sounds like u may not have compression on those cyl. , check em.

[m3BMW95]

Yeah, it runs perfect at full throttle, and idle sometimes. When I was cleaning the ICV, I think I got too rough with it, that is why I was wondering about that. If it were the valves, I would think that it would do it all the time, especially at full throttle. Sometimes it will do it all the times, other times you can't really notice it, it is wierd, off and on. Thanks for any advice

[Deadphan]

I had the same conditions when I had a few large vaccum leaks after my M50 mani install. Check for them.