Q: P0300 codes while idling

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I have been getting p0300 codes on my van this past week. The codes only appear while idling. I’ve checked and repaired a few vacuum lines, cleaned the mass air flow sensor, cleaned the throttle body, installed new plugs, cap and rotor, ran fuel injector cleaner through the fuel system, checked the for intake manifold leaks and more. So I decided to pull the plug on the mass air flow sensor and all of my misfires were gone. My van ran great with no problems! I bought a new mass air flow sensor and installed it. I cleared the mass air flow code and started it up. Less than a minute later p0300 codes showed up again. So I unplugged the new one and the misfires were gone. Can you tell me what’s going on? Should I return my new MAF sensor? Is this something I should worry about?

Hello. If unplugging the MAF sensor causes the engine to run better then there is a secondary air leak into the engine. This means that there is a vacuum leak from someplace. Most of the time on this engine it is from the intake manifold. It may also be a rich condition that can be from the fuel injection unit.

I usually check this by installing a scan tool to see what the fuel trim readings are. This will tell me if it is getting too much air or fuel and where to start. I have seen more intake manifold gasket failures on this engine than anything else. If you are going to have this repaired, consider YourMechanic, as a certified mechanic can come to you home or office to diagnose your Check Engine Light and repair it accordingly.

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