If unmeasured air enters engines equipped with L-type injection, they may exhibit lean surges, misfire and rough idle. Lean operating conditions can also cause increases in hydrocarbons, due to misfire, and in NOx due to leaner air/fuel ratios, increased combustion temperatures and decreased reduction catalyst efficiency.
Engines equipped with D-type injection will exhibit an elevated engine idle speed if unmeasured air enters the induction system. Generally, this will not cause exhaust emissions to increase significantly.
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