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Q: Engine keeps misfiring on humid days

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My car has engine issues only when the weather is humid. Then, it would start misfiring. I had the distributor cap replaced along with the rotor and plug wires as well. The car runs smoothly when the weather is warm and dry. However, despite these repairs, the engine keeps misfiring on very humid days. What should I do?

The humidity in the air will also affect the air pressure around your vehicle. When air pressure is affected, engine vacuum is also affected. The engine’s positive crankcase ventilation system relies on engine vacuum to function properly. If the engine vacuum is not sufficient, the PCV system may not work properly and allow the engine oil to reach the air filter. If the engine oil reaches the air filter, this can saturate the air filter and cause oil to be drawn into the throttle body with intake air. If this happens, the engine will burn oil and therefore have a misfire. I would recommend having your air filter and PCV system checked out to determine if any issues are present and start from there. A qualified mechanic, such as one from YourMechanic, can perform an engine misfiring diagnosis to determine how to proceed with a repair.

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