Hi, New to the board, Have a 2006 Sonata. That started to run a bit rough.Check engine light blinking and pulled up code P0300 multiple misfire 147k on car and plugs has not been changed. Im hoping its the plugs. Since going through the trouble pulling the platinum. Should I also replace the coil on the back 3 cyl? Thanks for any comments

 

Here is a comment ...
That's a lot of work for the back three spark plugs.
Should check the wiring since you will be in the neighborhood.
Which cylinder had the misfire?
Might want to check the coils also??

 

p0300 code random misfire, changed plugs and all is good. Had original plugs in it with 148k. Thanks for response

 

Thanks for coming back and updating.
It help me and others to know what the fix was.

 

Well back to the drawing board. Drove the car couple days then starts to stumble at certain speed, CEL blinks the code comes up with p0300 random misfire again. People that owed the car before me said CEL had been on for over a year. Had a code of p0504, bad brake light switch. cleared code then about 20 miles later. original misfire code came up.. I was thinking possible bad coil but should point out to effected cyl. Any ideas greatly appreciated

 

Okay, ideas ...
Vacuum leak .. take carb cleaner or brakes cleaner and spray around the intake manifold while the engine is running.
Any change in engine idle means there is a leak

Spark plugs and their wires.
Clogged fuel injectors.
Faulty fuel pump or clogged fuel filters.
Faulty down stream O2 due to rubbing wires bare.
Faulty TPS or crank sensor.

Now these are only ideas.
Don't go replacing anything unless you test it to know that is the problem or this can get quite expensive trying to fix this problem.

try something simple first like clean the in-take plenum

Note: if bad coil then try power balance test.
Take one wire off at a time (careful of electrocution) and look for change in rpm
That would point to the bad cylinder.

 

finally got it. only codes up was random misfire. hooked up a larger scanner and drove car around. finally picked up as having a bad coil on #2. and once in awhile 4 would show up. So I switched 2 with 6 then 6 came up as misfire. replaced 2,4 and 6 and has been running well. I was going to change 1,3 and 5 when I did plugs prior. Ill wait now until they become a problem.
Thanks for the reply

 

glad you got it fixed
thanks again for coming back and posting the fix