My engine was throwing a p0171 code. Mechanic told me both a/f sensors are bad. He cleared the code too. So new a/f sensors in it and mileage seems to be fixed (since it was too lean the car ATE gas) but the car idles really rough and wants to stall when I come to a stop. I've only driven the car about two miles with the new sensors, so how long can I expect this low idle to last?