The O2 sensor won't cause an idle issue like this...O2 sensors fine tune the fuel mixture under certain conditions.

Your problem is more likely caused by a vacuum leak.
Most common is a too tight throttle cable or sticking throttle body.
Another potential cause for your issue could be gasket related.
Either the throttle body gasket (you did use a new gasket, right?)
Or possibly the intake manifold gasket.
A leak at either will cause a high idle condition.