P0300 Diagnostic Code - Random Misfire
Po303 Diagnostic code - Misfire cylinder 3
Symptoms.
Engine may stumble or miss
Engine may be hard to start
you may notice no issues
Cause
Failing spark plugs or spark plug wires
Bad coil or coil pack
Failing oxygen sensor(s)
Bad fuel injector or more than one
Stuck exhaust valve
Bad catalytic converter
EGR valve or valve passage clogging
Bad camshaft position sensor
Bad PCM or ECM
The Fix
Best first action is a tune up, new plugs, wires, inspect all hoses and wire connections then reset the code. If it returns you will need to narrow it down to a system, coils and coil packs should be tested, catalytic converters for function ( do you smell rotten eggs?). A misfire that jumps cylinders could indicate a lean condition, do you have any other codes along with the 300? this will help clue you in to the source, check valve function to make sure they are opening and closing fully.
This is probably pone of the most difficult codes to troubleshoot, so start with the basics and work your way into the more expensive options, in many cases a good old tune up solves the problem, back it up with a fuel system cleaning and see where you stand.
Trouble code P0300 means:Random/multiple cylinder misfire detected
Trouble code P0303 means:Cylinder 3 misfire detected
P0422 talks about catalyst efficiency. P0300 is random multiple misfires. http://www.troublecodes.net/OBD2/Pcodes.shtml
A vacuum leak, a bad injector and if the check engine light is on, check the codes.
You have to find out what is causing random misfires in the engine. See related question below.
Read through the "Related Question" that discusses a common problem with the Windstars and rough idle - check engine codes P0171 & P0174. That might be part of your problem too...
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