The correct answer is D) malfunctioning governor. The governor is a device that regulates the engine speed by controlling the fuel supply to the engine. If the engine speed increases without a change in the engine control settings, it suggests that the governor is not functioning properly and is not able to maintain the desired engine speed. This could be due to a mechanical or electrical issue with the governor. The other options are incorrect because: A) A clogged intake air intercooler would not cause the engine speed to increase, but rather decrease the engine output. B) A control air leak would not directly affect the engine speed regulation. C) A leaking air starting valve would not impact the engine speed regulation during normal operation.