While a malfunctioning EGR valve *can* sometimes slightly decrease fuel economy, blocking it entirely removes a crucial part of the emissions control system. The engine will run richer (more fuel injected for the same amount of air), leading to:
* Reduced fuel efficiency: The engine needs more fuel to compensate for the lack of exhaust gas recirculation.
* Increased emissions: Blocking the EGR valve drastically increases NOx emissions, which are harmful pollutants.
* Potential engine damage: Higher combustion temperatures from the richer mixture can damage engine components over time. The EGR system helps cool combustion temperatures.
In short, leaving the EGR valve functioning correctly is essential for both good fuel economy and protecting your engine. If you're experiencing poor fuel economy, a blocked EGR valve is unlikely the cause and investigating other potential problems is recommended. Repairing or replacing a faulty EGR valve is the proper course of action if needed.
