Throttle Body: Adjustments

MINIMUM IDLE SPEED ADJUSTMENT (TBI)



WARNING: THE VEHICLE WHEELS MUST BE BLOCKED AND PARKING BRAKE APPLIED WHEN CHECKING IDLE SPEED.


IMPORTANT NOTES
NOTE: Minimum Idle Speed adjustments are set at the factory and MUST NOT be tampered with to alter minimum or maximum engine idle speed. Improper adjustment of the idle speed screw can cause false PCM codes, idle instability and automatic transaxle shift concerns, etc.

NOTE: Residue accumulation can cause stall after start with a warm engine, stall during acceleration or a sticky throttle on the vehicle's engine. Prior to adjusting Minimum Idle Speed clean the throttle body bore/valve in the area behind the throttle valve with the engine not running. Use a shop towel and carburetor cleaner that DOES NOT contain methyl ethyl keytone. The throttle body area can be cleaned by removing the air intake tube and holding the throttle full open. Use extreme care and do not scratch or damage the throttle body bore/valve. Check engine idle speed.

NOTE: Adjustments should be performed only when the throttle body has been replaced and/or when idle speed cannot be obtained. Engine should be at normal operating temperature (upper radiator hose is warm) before making adjustments.

NOTE: The idle stop screw is used to regulate minimum idle speed of the engine. On original equipment throttle bodies, it is adjusted at the factory, then covered with a plug to discourage unnecessary readjustment.

NOTE: On replacement throttle bodies, the idle stop screw is preset by the manufacturer and is covered with a plug.


PROCEDURE

1. Block wheels and apply parking brake.

Figure 1 - Hookup Of IAC Tester. (Typical):

2. Connect the IAC tester SA9195E, the SATURN PDT unit, or equivalent. The IAC pintle must be seated in the throttle body.

NOTE: A/C and cooling fans must be "OFF" when checking or adjusting idle air speed.

Figure 2 - Removal Of Idle Stop Screw Plug.:

3. If present, remove idle stop screw plug by piercing it with an awl, then applying leverage.

Figure 3 - Installing IAC Air Plug In The Throttle Body.:

4. Insert the IAC air plug in the throttle body.
^ SA9196E (or equivalent) used for TBI


5. Using SATURN PDT unit (or equivalent), Check idle speed, if not within specifications (550 +/- 100 rpm), adjust idle stop screw to:
^ 550 +/- 50 rpm

6. Turn ignition "OFF" and connect electrical connector to IAC valve assembly. Push in until a click is heard and pull back to confirm positive engagement.

7. Using SATURN PDT unit (or equivalent) check voltage on TPS. Do not replace TPS unless setting is outside of 0.35-0.70 volt limit.

8. Remove IAC air plug and install idle stop plug.

9. Start engine and check for proper idle operation.




IAC RESET PROCEDURE
The PCM resets the IAC valve pintle position only after a power is shut "OFF". During the reset, the PCM commands the IAC valve pintle to move In to the seated position (to establish the zero count position), and then back out to the desired position.

The IAC valve also can be reset without driving the vehicle by using the following service procedure:

1. Disconnecting the battery.

2. Use the service tool SA9195E (or equivalent) and run the pintle in.

3. Use the Portable Diagnostic Tester (PDT) (or equivalent) and command the pintle in.


SERVICE PRECAUTIONS
If the IAC valve is disconnected and connected while the engine is running, the resulting IAC valve counts may not correspond with the actual IAC valve pintle position. When servicing the IAC valve, it should only be disconnected or connected after the ignition has been turned "OFF" for at least 10 seconds. This allows time for the PCM to move the IAC valve to the 100 count position where it is parked while the ignition is "OFF". If this procedure is not followed, the PCM will lose track of IAC valve position resulting in starting or idle control problems until the IAC valve pintle position is relearned.




Idle Speed - Controlled RPM



Engine Trans. Gear RPM

Man./ Auto. Neutral 750 +/- 50

Auto. Drive 650 +/- 50

Auto. Drive 775 +/- 50
(With A/C "ON")

Air Flow Through Throttle Body.:

IDLE SPEED CONTROL OPERATION
Engine idle speed is controlled by the PCM through the IAC valve, mounted on the throttle body. The PCM sends voltage pulses to the IAC valve motor windings causing the IAC valve pintle to move In (toward the seat) a given distance (a step or count) for each pulse. The commanded location (steps away from the seated position) can be observed as a number of counts, as displayed on a Scan tool. The pintle movement controls the airflow around the throttle valve, which in turn, controls engine idle speeds:

^ Pintle Extended = Decrease rpm - Lower Counts.

^ Pintle Retracted = Increase rpm - Higher Counts.

The controlled or desired idle speed for all engine operating conditions is programmed into the PCM. The programmed engine speeds are based on coolant temperature, park/neutral switch status, vehicle speed, battery voltage, and A/C (if equipped).



IDLE LEARN
The PCM learns the proper IAC valve positions to achieve warm, stabilized idle speeds (rpm) in drive. This information is stored in the PCM Keep-Alive memories (information is retained after ignition is "OFF"). All other IAC valve positioning is calculated based on these memory values. As a result, engine variations due to wear, and ariations in minimum throttle valve position (within limits) do not affect engine idle speeds. This system provides correct idle control under all conditions. If power to the PCM is interrupted, the PCM has to relearn idle control. Until idle control is relearned, it may be necessary to partially depress the accelerator pedal when starting. This also means that disconnecting power to the PCM can result in incorrect idle control or necessity to partially depress the accelerator when starting, until the PCM relearns idle control. Refer to information regarding clearing memory under COMPUTERS AND CONTROL SYSTEMS. Engine idle speed is a function of total airflow into the engine based on IAC valve pintle position plus calibrated vacuum loss through accessories.

The minimum throttle valve position is set at the factory with a stop screw. This setting allows enough air flow by the throttle valve to cause the IAC valve pintle to be positioned a calibrated number of steps (counts), from the seat, during controlled idle operation. The minimum throttle valve position setting on this engine should not be considered the minimum idle speed, as on other fuel injected engines. Low internal friction, provisions for slight production variations, and due to the various altitudes production vehicles may operate at the calibrated air rate at the minimum throttle position is too low to allow most engines to idle. The throttle stop screw is covered with a plug at the factory, following adjustment. It should only be readjusted when all other checks have been completed and the idle condition could not be corrected. Adjusting the throttle stop screw probably will not correct an irregular idle condition.

Engine idle speed is a function of total air flow into the engine based on IAC valve pintle position plus throttle valve opening, plus calibrated vacuum loss through accessories.