Originally Posted by oldford

P0135 - O2 Sensor Heater Circuit Bank 1 Sensor 1
P1131 - Lack Of HO2S11 Switches - Sensor Indicates Lean
P1518 - Intake Manifold Runner Control Stuck Open (Bank 1)

P1131 is probably caused by P0135. Because the sensor heater doesn't work, there are times where there's no signal from the O2 sensor.