Furnace clean and tune. Cycled system. Checked heat exchanger. Found all chambers have some rusting and corrosion. No cracks found visibly. Checked, removed, and cleaned burners and flame sensor. Both ok. Found igniter to be getting worn. Whiting found on igniter surface, no cracks found at this time. Checked and tightened electrical connections and clamps. Cleared drain lines, no obstruction found in lines or pressure tubes. Checked and adjusted gas pressures to maximize efficiency. Preformed combustion test. Normal levels found in exhaust. No CO found in airstream. System showing some signs of getting worn, but system operating normal at this time. Job complete.