I have a 2008 RX350 with 68k on the clock. received a check engine light for random misfire (P0300) and misfire on Cylinder 4 (P0304), Cylinder ,5 (P0305) ,Cylinder 6 (P0306). Question is what will be causing this to happen.

I thought about changing the spark plugs to see if this is possibly the cause. but what else should i be checking?

 

You may just be un-lucky and have three bad coil packs. I will tell you if they are original equipment, I don't think the plugs are an issue as the iridium OE plugs are extremely reliable. Coil packs do fail however. You can swap them on the front cylinder and see if the codes change. Keep track of where you put them (mark them with blue masking tape with location) and see if the code moves. Good luck.