Last week going into work pulling away from the light I got to around 40 and shifting into 5th all hell broke loose. Like someone flipped a switch the car just instantly fell on its face and ran super rough. Ultimately after making it home that night I pulled the valve cover and found after zero compression that the rocker arm on cylinder 4 intake valve fell off and the valve was hung open. lightly tapped on the valve stem and the valve popped right back up. Yesterday I took the spring and seal off and found nothing abnormal, no excesssive endplay, valve was smooth and not even a hint of binding. This head has the aftermarket valve guides with the circlip so they dont fall supposedly. Valve fully closes so the seat is ok. just a random freak occurance ? Put it back together last night and everything has been ok so far.