The heater problem could be due to insufficient coolant in system or the thermostat is not closing properly. Have it checked and replaced if necessary.
As to the sputtering after warming up, if the idling speed is too low, it would tend to want to stall. It should not be associated with the catalytic converter but more likely a misfiring and it could be due to a failing ignition coil or spark plugs.
Sunday, May 22nd, 2011 AT 7:35 PM