The 300 series diagnostic codes for your car relate to the Aux Emissions Controls. For the 327 diagnostic code, the recommendation is to check the EGR valve operation.
Pasted below is the initial test step for EGR valve operation from the factory service manual.
- Install a tachometer, Rotunda 059-00010 or equivalent.
- Disconnect the Idle Air Control (IAC) solenoid (9F715) electrical connector.
- Remove and plug the vacuum supply hose from the EGR valve nipple.
- Start engine, idle with transmission in NEUTRAL, and observe idle speed. If necessary, adjust idle speed according to «Section 9A».
- NOTE: If the engine will not idle with IAC solenoid disconnected, provide an air bypass to the engine by slightly opening the throttle plate or by creating an intake vacuum leak. Do not exceed a typical idle rpm.
- Slowly apply 5-10 inches of vacuum to the EGR valve nipple using a hand vacuum pump, Rotunda 021-00014 or equivalent.
- Does idle speed drop more than 100 rpm with vacuum applied and return to normal (± 25 rpm) after the vacuum is removed?
Yes
The EGR valve is OK.
UNPLUG and RECONNECT the EGR valve vacuum supply hose.
RECONNECT the IAC solenoid connector.
REFER to Diagnostic Routines, «Section 2A».
No
INSPECT the EGR valve for blockage or contamination.
CLEAN the valve using Rotunda 021-80056 EGR valve cleaner.
INSPECT valve for vacuum leakage.
REPLACE if necessary.
-Rod