On the 1995 Lexus SC300, the Code 24 points to a problem with the Intake Air Temp (IAT) Sensor. The Code 31 points to a fault with the Mass Air Flow (MAF) Sensor. On this vehicle, the intake Air Temp Sensor is built into and part of the MAF Sensor. So, carefully inspect the electrical connector to the MAF/IAT Sensor for any loose, broken or damaged wires. Inspect the air filter and make sure it is not excessively dirty and restricting air flow. Make sure the air filter housing is sealed tightly and correctly. Make sure there are no holes or rips in the air duct. If all of these check ok, replacing the MAF/IAT Sensor should solve the problem. You can find the MAF/IAT Sensor mounted near the Air Filter Housing.
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