My 1991 vw caravelle automatic 2.1 L MV engine has had a bumper to bumper checkup ,repair and tune up.But the mileage is still very poor.engine compression is good runs smoothly and performance is good.Mileage is only 300 kms for a full tank.Is this normal for auto transmission van?Do I need to check the E.C.U. ?Sometimes the throttle position switch plays up causing the engine idle to vibrate, could this be the reason?