My 2001 lexus rx300 is idling rough. Scan showed 4 cylinders not firing right.

What is your question?

Changed plugs. it seems to run ok till warmed up. Then it idles rough. Sometimes the power brakes do not work. VCS light is on. It was running rough on one cylinder till I had rear valve cover replaced. Now it is bad on four.

What makes this problem better or worse?

iIt is worse when warm.