EGR Valve Operation

SENSORS AFFECTING COMPUTER CONTROL OF EGR OPERATION
The PCM uses the following sensors to control the EGR solenoid:

^ Engine Coolant Temperature (ECT)
^ Throttle Position (TP)
^ Manifold Pressure (MAP)
^ Intake Air Temperature (IAT)
^ Throttle Switch (ISC)
^ RPM data from distributor reference pulses.
^ Vehicle Speed Sensor (VSS)

DRIVEABILITY PROBLEMS WITH TOO MUCH EGR
During cold operation and at idle, the solenoid circuit is grounded by the PCM. This blocks vacuum to the EGR valve. Too much EGR flow tends to weaken combustion, causing the engine to run roughly or stop. With too much EGR flow at idle, cruise, or cold operation, any of the following conditions may occur:

^ Engine stops after cold start.
^ Engine stops at idle after deceleration.

DRIVEABILITY PROBLEMS WITH TOO LITTLE EGR
If the EGR valve should stay open due to a stuck open valve all of the time, the engine may not run. Too little or no EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:

^ Spark knock (detonation).
^ Emission test failure.
^ Car surges during cruise.
^ Rough idle.