my 2000 3.4l impala is running lean. Live data scan shows a 21.8 air fuel ratio which is way up. All my vacuum lines are in good shape and nothing appears wrong on top. would a lower intake gasket cause a lean code to show up. Also, on the scan the only code I get is bank 1 system lean. Bank 2 doesn't throw a code. Could that mean that it's the o2 sensor. The car has 162k on it and they are the factory sensors. Car was in Chicago for the first 100k and Florida for the rest. The intake manifold gasket where changed once already at about 95k miles. And help and ideas would be great. Thanks.