If you’ve noticed your engine surging or hesitating for no apparent reason, you could have a problem with your exhaust gas recirculation, or EGR.  This system is designed to send a portion of the vehicle exhaust back through the engine to reduce emissions.  A carbon buildup blocks the passages through the EGR valve, causing problems in the engine.  In addition to low fuel economy, the car will eventually be difficult to start and will run poorly.  If you've noticed any of these problems, schedule an appointment to have your vehicle inspected.