My prius (189k on the ODO) started shuddering all of a sudden as I was driving and the check engine light started flashing on and off. The CEL has not remained solid. The shuddering got worse under acceleration. I immediately checked the coolant level and it is still at the full mark. Where should I begin? Replacing the coils, spark plugs, egr valve, egr cooler, intake manifold? Took a picture of the dipstick... someone said it sounds like it's out of oil but it seems like there is plenty. Also, if anyone is near Yorktown VA, I would love some help as I do it and can offer compensation to mane sure I don't miss things. Thanks!