My wife's car 2002 XG350L started idling funny. When the brake was pressed it would idle very low and act like it wanted to cut off. When placed in park the car would idle high. Also when driving, it would sputter. Our local mechanic said if might be the mass airflow sensor or something related to it. I've priced the parts and it seems to run anywhere for $200 to $300 for the part alone (no labor included). If it is not the mass airflow sensor itself then what could it possibly be?