it is only when i am idling at a stop, i have recently cleaned the mass air flow sensor and consistently run mid grade fuel as i was having problems with it running to lean. just recently ran risolone fuel system cleaner/lubricator through but normally use another brand. codes p0300 and p303 pop up when the diagnostic was ran.
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2002 Chevrolet Prizm Question: p0300 and p0303 random multiple cylinder misfire, whats the most common causes?
Answer #1mastertech6371 August 19, 2011, 15:04Master
i would start with basics. plugs, wires. that is the most common failure. after that, i would get a real diag from a real shop.
Answer #2chinasinoy August 20, 2011, 05:49Journeyman
If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.