Engine Control System - On-Vehicle Adjustments Buick Century VI

ENGINE MECHANICAL

Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.

VALVE CLEARANCE

Note. All engines except Vibe 1.8L, use hydraulic lifters. Adjustments are not required. For Vibe 1.8L specifications, see VALVE CLEARANCE SPECIFICATIONS - VIBE 1.8L table.

VALVE CLEARANCE SPECIFICATIONS - VIBE 1.8L

IGNITION TIMING

Note. All engines are equipped with either a C 3 I, DIS or IDI ignition system. Timing on these systems is controlled by the Powertrain Control Module (PCM) and is not adjustable.

IDLE SPEED & MIXTURE

Note. Idle mixture is controlled by the Powertrain Control Module (PCM). Adjustment is not possible. After replacement of Idle Air Control (IAC) valve, system must be cycled as identified for PCM to properly control idle speed. If idle speed is not okay after cycling system, problem is usually caused by a dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.

1.8L (Vibe)

The Powertrain Control Module (PCM) determines the correct engine idle speed by using input from various sensors and switches in order to assess the engine status and requirements. The engine idle speed is controlled by the PCM through the idle air control (IAC) valve.

The PCM has a relearn process which enables the control module to make corrections for minor variations in the fuel system. This learning ability can improve driveability. Disconnecting the battery resets the learning process. A change in the vehicle's performance may be noticed when a reset from a PCM power down occurs. Operating the vehicle under varying conditions will enable the control module to regain any lost vehicle performance.

In order to initiate the control module learning ability, warm the engine to operating temperature and drive the vehicle at part throttle with moderate acceleration. Continue to drive the vehicle while including steady cruise and idle speed operation. For the best idle speed quality several key cycles with a short drive and long idle periods is recommended.

2.2L (L200 & LW200)

Turn ignition ON for 10 seconds. Then turn ignition OFF for 10 seconds. Start engine and let idle for 30 seconds. Accelerate engine slowly between idle and 3500 RPM 5 times. Let engine return to idle. IAC valve position should be relearned. PCM will now properly control idle speed.

2.2L (Alero, Cavalier, Grand Am, Ion & Sunfire), & 2.4L (Cavalier & Sunfire)

Note. Information for bi-fuel Cavalier is not available.

Turn ignition ON with engine OFF. Turn ignition OFF for 10 seconds. Start engine and check for proper idle operation. PCM will now properly control idle speed.

3.0L (L300 & LW300)

This engine is equipped with a Throttle Actuator Control (TAC) system. No idle speed adjustment is possible.

3.1L (Century, Malibu & Grand Prix), 3.4L (Alero & Grand Am) & 3.8L (Bonneville, LeSabre & Park Avenue)

Turn ignition ON, then OFF. Turn ignition ON, then OFF again. Start and operate engine until normal operating temperature is reached. PCM will now properly control idle speed.

3.2L (CTS)

1. Ensure that the following conditions are met: The vehicle speed is zero MPH. The accelerator pedal angle is less than 14.9 percent. The battery voltage is more than 10 volts. The engine coolant temperature is between 41-140°F (5-60°C). The intake air temperature is more than 41-140°F (5-60°C).
2. Turn OFF the ignition for 30 seconds.
3. Turn ON the ignition, with the engine OFF for 1 minute.
4. Turn OFF the ignition.
5. Clear DTCs as necessary.

3.4L (Impala & Monte Carlo) & 3.8L (Grand Prix, Impala, Monte Carlo & Regal)

Turn ignition ON, then OFF. Turn ignition ON for 10 seconds, then OFF for 5 seconds. Start and operate engine until normal operating temperature is reached. PCM will now properly control idle speed.

4.0L (Aurora) & 4.6L (DeVille & Seville)

Start and operate engine at idle for 15 seconds. Turn ignition OFF. Wait 15 seconds. Restart engine. PCM will now properly control idle speed.

5.7L (Corvette)

Throttle control is electronic with NO mechanical link from engine to accelerator pedal. The PCM and Throttle Actuator Control (TAC) module monitors the position of accelerator pedal based on signals from a nonadjustable Accelerator Pedal Position (APP) sensor. Idle speed is preset at the factory and is not adjustable.

THROTTLE POSITION SENSOR

Note. TP sensor is not adjustable, however, on some models the following learn procedure(s) must be performed. Other models relearn during drive cycle. For further testing procedures, refer to appropriate SELF-DIAGNOSTICS or SYSTEM & COMPONENT TESTING article.

Note. On some models, throttle control is electronic with no mechanical link from engine to accelerator pedal. The PCM and Throttle Actuator Control (TAC) module monitor the position of accelerator pedal based on signals from a nonadjustable Accelerator Pedal Position (APP) sensor. The APP is mounted above the accelerator pedal. For further testing procedures, refer to appropriate SELF-DIAGNOSTICS or SYSTEM & COMPONENT TESTING article.

Throttle Position Sensor Learn Procedure (4.6L - Deville & Seville)

TP Sensor learn procedure

1. Turn the ignition to the RUN position.
2. Wait 1 minute.
3. Turn ignition switch to the LOCK/OFF position.
4. Wait 15 seconds.

See also:
• VALVE CLEARANCE SPECIFICATIONS - VIBE 1.8L