System Diagnosis

A leak in the EGR vacuum system can upset the control modules programmed control of exhaust gas recirculation and adversely affect engine operation. Too much exhaust gas recirculation at idle or cruise with a gasoline engine can result in the engine stalling after closed throttle deceleration, surging during steady throttle cruising or a rough idle. Too little exhaust gas flow allows combustion temperatures to become too high and bring about detonation ("spark knock") or an overheated engine. In addition, nitrous oxide emissions may be high enough to cause the vehicle to fail an emissions test.

Because the source of an EGR system symptom might be traced to a mechanical or electrical condition as well as a faulty vacuum system, an effective systematic diagnosis procedure should examine all three categories of components - not just the vacuum system alone. Therefore, no exclusive vacuum system diagnosis procedures are provided here. Refer to
EMISSION CONTROL SYSTEMS section for more information.