The Nissan Altima uses a digital electronic exhaust gas recirculation, or EGR, valve as part of its emissions system. The valve works to reduce harmful gas emissions due to fuel combustion and also lowers temperatures inside the engine for more efficient fuel burning. When this valve malfunctions, its symptoms can mimic several other common conditions, like air leaks.
If the EGR valve in the Altima is stuck in its open position it may cause the vehicle's engine to run rough when idling. The vehicle may also stall out due to spent emissions flowing back into the engine from the vehicle's exhaust system. These symptoms are often interpreted as a vacuum leak according to AA1Car, an automotive repair website. The Altima's electronic control module should emit a fault code that corresponds to the EGR valve. A digital diagnostic tool can be used to read the fault code and determine if the problem is caused by a vacuum leak or the EGR valve.
Spark knock is a rattling or metallic pinging noise that comes from an engine when it is accelerating or under strenuous activity. This means the fuel entering your engine is actually exploding instead of burning evenly. An EGR valve that is corroded shut can cause this condition in a Nissan Altima. The closed valve allows combustion temperatures within the engine to rise, which leads to the spark knock condition. Spark knock can cause failure of the engine's head gasket and damage to pistons and bearings.
A damaged digital EGR valve, like those used in modern Nissan Altimas, may cause the engine to hesitate during acceleration. Hesitation is caused by the mismanagement of airflow entering the engine and exhaust gas leaving the engine. The damaged valve can also cause the engine to misfire due to premature combustion. This condition is similar to spark knock, though less severe. Hesitation and engine misfire may be misinterpreted as a vacuum leak in a similar manner as rough idling and engine stalling.
