I've been trying to hunt down a poor mileage issue. The O2's arent cycling at idle, however, the cycle nicely while driving. Bank one at idle will show very lean and start dumpin fuel, which in city driving, is killing gas mileage. The bank 1 O2 is a brand new Bosch also. It does it with a tune from RPM in, as well as a stock tune. I replaced the header gasket since it showed signs of leaking, and checked for other leaks, but none found.
Any ideas?