What condition can a defective automatic mixture control unit lead to?

A defective automatic mixture control unit can lead to a lean fuel mixture. This occurs because the unit is responsible for maintaining the optimal fuel-to-air ratio for combustion in the engine. If the control unit malfunctions, it may not deliver enough fuel, which results in a higher proportion of air compared to fuel in the mixture.

A lean mixture can lead to various operational issues, including engine knock, increased combustion temperatures, and poor performance. The engine requires a specific balance of fuel and air for efficient combustion; when this balance is disrupted due to a faulty control unit, the vehicle can suffer from suboptimal performance.

In contrast, the other conditions listed – such as increased throttle response or a rich fuel mixture – are not directly associated with the failure of the automatic mixture control unit. A stable meter pressure, while desirable, does not address the critical aspect of fuel mixture balance that a defective unit influences.