I am getting no more than 15 MPG on my 89 535i, city driving of course. Recently had her serviced with new plugs (Bosch +4 plat.), wires set, cap'n rotor, valve adjustment, Mobil 1. The car seems to have no other problems. Smooth idling, smooth acceleration. Why 15 MPG? I drive very conservatively. My right foot is very light.
What's next? Want to replace O2 sensor by myself. Is it possible without special tools? Is there just one near the Cat and no more? Some company sells the 'O2 senor Kit', which replaces just the core (i guess that is the sensor). is that good? it sounds better to replace the whole unit. anyways. any comments or advises will be appreciated.