The misfire fault (p0300 for random misfires or p 0301-08 for individual cylinder misfires) is seldom as a result of plugs
It is more likely from
low fuel pressure ,pump , EVAP not venting ,dirty injectors , wiring to the injectors , injector control, or ECM
simple fix is to put a can or 2 of injector cleaner in the tank and go for a good drive
next is to replace the fuel filter
more involved is to have the fuel pressure tested to check for pump and pressure regulator operation
SOURCE: spark plugs on 2002 Saturn vue
just completed a plug removal and install on my '02 awd v6. if you have the time and patience it's straight forward; common sense was most helpful. to gain access to the plugs, both fore and aft, you must remove, in short, everything near to, associated with, the air intake system. common tools plus a 1/4 socket, with 8 inch extension to hold a #10 star bit. these star bolts are under the rectangular plastic plate atop the intake. once you have those out, disconnect all the wiring, carefully. lift the intake out, look for plug covers, fore and aft, ignition assembly lays atop each row of three plugs. with the hands of a surgeon, remove the ignition assembly, and by golly ye shall see your reward. easy from then on.
replaced my plugs with the iridium 'honeys'; marked improvement in starting, acceleration, smoothnes, noise, and gas mileage to the value of + 3.0%. changed out the oil with mobile1 extended performance, changed transmission fluid. took a shower. time involved, 7.0 hrs. dealer be damned,,priceless!
SOURCE: 2004 Saturn VUE (M/T) STEADY service engine soon light
SOME TIME PCM GET A VOLTAGE SPIKE.OR ELECTRICAL INTERFERENCE WILL CAUSE SERVICE LIGHT TO COME ON WITH NO CODES.IF IT KEEP HAPPENING TAKE IT TO DEALERSHIP TO CHECK IT OUT.
SOURCE: 2002 Saturn SL1 check engine light code P0303
For old models, Saturn/GM also used the same material
fiberglass gasket in your model, you almost certainly have a leak from
a crumpled, sucked-in gasket as I suffered (and many others). I would
say going to Saturn dealership to make repairs is probably not good
idea if they are going to put in the same GM intake gasket part. Maybe
possible to specify Felpro gasket with whatever shop you go to if you
don't do the repair yourself. I would not go too long with your car in
that condition as there is localized leaning at your cyl-3, that could
cause a burnt exhaust valve there.
The exhaust is extra hot venting out
that cylinder. P0303 is misfire at cyl-3. Mine was P0301 (cyl-1). You
may get P0507 once in a while when PCM fails to control the fast idle
caused by the leak under certain conditions. Most of the time, it is
very slow idle caused by 3 cylinders running. You run smoother in cold
idle because the IAC opens up to increase idle and end up lowering the
manifold vacuum, so the reduced vacuum causes less leaking at the
failing intake manifold gasket.
I'd say try cleaning everything with your ignition before replacement; Idle problems could be caused by engine coolant sensor (ECTS). Are you sure it was changed? Did they put on a new wire connector along with it?
Hope helps.
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