Idle Speed: Adjustments

NOTE: The curb and fast idle speeds are controlled by the Engine Control Assembly (ECA) and the Idle Speed Control Bypass Air Valve (ISC-BPA). The ISC-BPA valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow this device to control the speed.
The idle speed setting procedure has been revised considerably to reflect the expanded application of the Self-Test idle speed options and because the throttle body incorporates an orifice in the throttle plate to control idle airflow as part of the sludge tolerant design.

Service Decal Location (Typical Throttle Body):

Throttle bodies with sludge tolerant design (introduced 1991 1/2 model vehicles) are clearly identified with a Yellow/Black decal. This decal warns that the throttle plate stop screw must not be adjusted counterclockwise (backed off), as this will not reduce the engine speed but may cause the throttle plate to stick in the bore. Backing out the screw may be required, if the throttle body has been previously serviced (a plug in the throttle plate orifice may be present), or the plate stop screw tampered with (TPS Self-Test output out of range). The decal also warns that the throttle body must NOT be cleaned inside the bore, as this cleaning will impair the sensitive coating. The sludge accumulation will not affect the idle air flow. The cleaning procedure for the ISC-BPA still applies.


REMEMBER
A change in idle airflow can occur not only at the throttle body but other areas as well. You should enter the idle speed procedure only after other possible causes in the following areas are eliminated.
^ Contamination within the idle speed control device
^ Lack of fuel system control (excessively rich or lean)
^ Throttle sticking or binding
^ Engine not reaching operating temperature
^ Incorrect ignition timing
^ Incorrect or clogged PCV system
^ Vacuum leaks (intake manifold, vacuum hoses, vacuum reservoirs, power brake booster etc.

VERIFY
^ Transmission is in PARK (A/T), or NEUTRAL (M/T)
^ Parking brake is applied (automatic brake disconnected where applicable)
^ Wheels blocked
^ Engine at operating temperature
^ Proper fuel pressure and no exhaust smoke
^ Correct and clean PCV system
^ Heater, A/C, and other accessories OFF
^ Ignition timing is set to specification
^ EEC-IV diagnostics have been performed and vehicle malfunction indicated service output codes have been resolved.


NON-E40D TRANSMISSIONS

STEP 1
With the engine OFF, connect a tachometer, according to manufacturer's instructions. Disconnect the negative (-) terminal of the battery for 5 minutes, then reconnect it.
STEP 2
START the engine and stabilize for two minutes. Goose the accelerator and let engine return to idle. Lightly depress and release the accelerator, then let engine idle.
STEP 3
If the engine is not idling properly, proceed with this procedure.
STEP 4
Unplug the in-line SPOUT connector. START the engine, and verify ignition timing is at base +/- 2~ BTDC.
STEP 5
With the engine OFF, install .050" - A/T (.030" - M/T) feeler gauge between the throttle plate stop screw and the throttle lever.
STEP 6
STOP the engine, and disconnect idle speed control air bypass solenoid.
STEP 7
START and RUN the engine at idle for 120 seconds.
STEP 8
Place the transmission in PARK (A/T), or NEUTRAL (M/T).
STEP 9
Using a tachometer, verify idle speed is at 675 +/-150 rpm (A/T), or 700 +/-150 (M/T).

NOTE: If the throttle plate stop screw must be turned in, turn OFF the engine, make estimated adjustment, START the engine, and verify adjustment. Repeat as necessary.

Throttle Plate Orifice Plug:

NOTE: A plug in the throttle body orifice will decrease idle rpm. Where as an orifice without a plug will increase idle rpm. Orifice plugs and installation tools are available in service kit # FOPZ-9F652-A.


RPM TOO LOW
DO NOT clean the throttle body, check the plate orifice plug. If there is no plug, turn the screw clockwise to the desired rpm. If there is a plug from previous service, remove the plug, then adjust the screw in either direction as required. Screw must be in contact with the lever pad after adjustment.

RPM TOO HIGH
a. Turn OFF the engine.
b. Disconnect air cleaner hose.
c. Temporarily block the orifice in the throttle plate with tape. If the orifice already has a plug from previous service, proceed to Step (e).
d. RESTART engine and check idle speed, using a tachometer.
NOTE: On vehicles with Mass Air Flow Sensors, reconnect the air intake duct hose before checking rpm. If the engine stalls, crack open the plate stop screw, but DO NOT over adjust.
e. If rpm continues to be fast, perform KOEO Self-Test.
^ If TPS output code is within range, remove tape from throttle body and check for other possible causes.
^ If TPS output is out of range, adjust screw for proper TPS code. Lever must be in contact with the screw.
^ If rpm is still fast, terminate this procedure and check for other possible causes.
f. If rpm drops to 675 rpm (A/T), or 700 rpm (M/T) or lower, or the engine stalls, turn OFF the engine, disconnect the air cleaner hose, and remove tape from throttle plate.
g. Install the plug with proper color code, depending on throttle plate orifice size.
h. Reconnect the air cleaner hose. START the engine, and check the idle rpm using a tachometer. Turn the plate stop screw clockwise to 675 +/-25 rpm (A/T), or 700 +/-25 rpm(M/T).

NOTE: DO NOT turn the plate stop screw counterclockwise. This may cause the throttle plate to stick at idle.
STEP 10.
Run the KOEO Self-Test for proper TPS code output.
STEP 11.
Turn OFF the engine, and disconnect the battery for at least 5 minutes.
STEP 12.
Remove the feeler gauge from throttle plate stop screw and lever pad.
STEP 13.
Reconnect the in-line SPOUT connector.
STEP 14.
Reconnect the Idle Speed Control Air Bypass Solenoid. Verify that the throttle is not sticking in the bore, and the linkage is not preventing the throttle from closing.
STEP 15.
START the engine and idle for two minutes. Goose the accelerator, and let the engine return to idle. Lightly depress and release the accelerator, then let engine idle.

NOTE: Engine rpm oscillations may be caused by the throttle plate being open far enough to expose the canister purge ports. To verify this, isolate the canister from the engine by disconnecting the hose at the port. Cap the throttle body purge port. If the oscillations cease, verify throttle cable has proper slack. If so, adjust the throttle plate.
STEP 16.
On Automatic Overdrive (AOD) Transmission applications, check TV pressure adjustment.

E40D TRANSMISSION EQUIPPED
PROCEDURE - SCAN TOOL REQUIRED

STEP 1
Activate engine running Self-Test
STEP 2
After service code 11 or 111 has been displayed, unlatch and within 4 seconds latch the STI button.
STEP 3
A single pulse code indicates the entry mode, then observe the Self-Test Output (STO) of the scan tool in Step 4. If adjustment is required in Step 4, ensure all other causes have been addressed and corrected before continuing.
STEP 4
a. A constant tone, solid light or "STO LO" readout means base idle rpm is within range. To exit test, unlatch STI button, then wait 4 seconds for reinitialization (after 10 minutes it will exit by itself).
b. Beeping tone, flashing light, or "STO LO" readout at (8 Hz) indicates Throttle Position Sensor is out of range due to over adjustment; adjustment may be required.
c. Beeping tone, flashing light, or "STO LO" readout at (4 Hz) indicates base idle rpm is too fast, adjustment is required, go to Step 6.
d. Beeping tone, flashing light, or "STO LO" readout at (1 Hz) indicates base idle is too low, adjustment is required, go to Step 5.

Throttle Plate Orifice Plug:

STEP 5 - RPM TOO LOW
DO NOT clean the throttle body. Check the plate orifice plug. If there is no plug, turn screw clockwise until conditions in Step 4 are satisfied. If there is a plug from previous service, remove the plug and adjust screw in either direction as required. Screw must be in contact with the lever pad after adjustment.
STEP 6 - RPM TOO HIGH
a. Turn OFF the engine.
b. Block the orifice in the throttle plate temporarily with tape. If the orifice already has a plug from previous service, go to Step (d).
c RESTART the engine and check idle speed using Self-Test (Mass Airflow models require the air intake hose to be reattached first). If the engine stalls, crack open the plate with the throttle plate stop screw.
d. If rpm continues to be fast, perform test in Step 7.
^ If the TPS output code is within range, remove tape and check for other causes.
^ If out of range adjust screw for proper TPS code (lever pad must be in contact with screw after adjustment).
^ If rpm is still fast, terminate this procedure and check for other possible causes.
e. If rpm drops to or below the desired level, as indicated by Self-Test Output tone, turn the engine OFF, disconnect air cleaner hose and remove tape.
f. Install the plug with the proper color code depending on the throttle plate orifice size.
g. Reconnect the air cleaner hose. START the engine, and turn the plate stop screw clockwise (DO NOT turn it counterclockwise as this may cause the throttle to stick at idle) until the conditions in Step 4a are satisfied.
STEP 7
Run the Key ON Engine OFF (KOEO) Self-Test for proper TPS output code.
STEP 8
Verify the throttle is not sticking in the bore, and the linkage is not preventing the throttle from closing.


PROCEDURES FOR PLUG INSTALLATION

STEP 1
Remove air inlet tube(s) from throttle body.

Throttle Plate Orifice Plug:

STEP 2
Select the proper color plug by using the Go/No-Go gauge pegs, included in the service kit (FOPZ-9F652-A).
STEP 3
Starting with the largest diameter gauge peg, attempt to insert through the throttle plate orifice.
STEP 4
If gauge peg goes through the orifice, use the corresponding color plug.
If gauge peg does not go through, proceed with the next smaller gauge peg for Go/No-Go Test.

NOTE: It is important that the largest Go/No-Go combination is used to determine the proper plug size.
STEP 5
If the smallest gauge peg does not go through the orifice, use the reamer bit and handle included with the service kit to enlarge the plate orifice. Wipe bearing grease on both sides of the plate orifice and on the reamer bit to hold the brass chips. After reaming, wipe plate clean and then return to Step 3 to determine the proper plug size.
STEP 6
Using the installation tool from the service kit, push the plug into the orifice until bottoming out at the throttle plate.
STEP 7
Open and snap closed the throttle several times to verify proper plug retention.
STEP 8
Reconnect the air inlet tube(s).
STEP 9
Reset idle rpm per engine requirement using the throttle plate stop screw.