Would a bad EGR valve or PCV valve cause engine oil blow back?

Yes, a bad EGR (Exhaust Gas Recirculation) valve or a faulty PCV (Positive Crankcase Ventilation) valve can contribute to engine oil blowback. A malfunctioning PCV valve can cause excessive pressure in the crankcase, which may lead to oil being pushed out of seals and gaskets. Similarly, a defective EGR valve can disrupt the engine's air-fuel mixture and combustion process, potentially leading to oil leaks or blowback. Properly functioning valves are essential for maintaining engine pressure and preventing oil from escaping.