My Toyota Avalon 02 is experiencing problems with check engine light flashing when idling at a light and then goes solid when driving. The codes read p0300 Thru p0303. The car idles very rough and shakes...
code p 300 is random misfires
code p 0301,-2,-3,-4,-5,-6,-7,-8 all refer to the cylinder that is misfiring ie p 0303 is no 3cyl misfiring
many people mistakenly believe that a misfire is from the plug, wires distributor when in fact it is more likely to be a problem injector ---dirty tip , low fuel; pressure , blocked tip, injector wiring
using gas conditioner sometimes works but in many cases it dislodges gunk that blocks the tip
At this point I would get a fuel pressure test done to check the pressure regulator , pump and filter condition as everything you describe points to fuel and injectors
AS a point of interest- with ECM controlled engines, the ECM tunes up the engine 60 times a minute to keep it within parameters and the plugs will last the life of the engine
when you want to do a tune up , simply have the fault codes read and fix only what comes up