Idle Speed: Adjustments
NOTE: The curb and fast idle speeds are controlled by the Powertrain Control Module (PCM) and the Idle Air Control (IAC) valve. The IAC 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.
Throttle Body Assembly:
Throttle bodies with sludge tolerant design are 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 IAC 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.
IDLE SPEED CHECK PROCEDURE
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, then goose the engine and let it return to idle, lightly depress and release the accelerator and let engine idle.
STEP 3
If the engine is not idling properly, turn the engine Off, and disconnect Idle Air Control (IAC) solenoid.
STEP 4
Place the transmission in Park (A/T), or Neutral (M/T).
STEP 5
Start the engine, then using a tachometer, verify idle rpm is 600 +75/-50 rpm.
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 # F0PZ-9F652-A.
STEP 6
RPM TOO LOW
a. Do not clean the throttle body, check for the plate orifice plug.
- If there is no plug, turn the screw clockwise to the desired rpm +/- 25 rpm.
- If there is a plug from previous service, remove the plug, and adjust the screw in either direction as required.
NOTE: Screw must be in contact with the lever pad after adjustment.
RPM TOO HIGH
a. Turn engine Off.
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), otherwise proceed with next step.
d. Restart the engine, and check the idle speed, using a tachometer.
NOTE: For vehicles with Mass Air applications, reconnect the air intake duct hose before checking the rpm.
If the engine stalled, crack open the plate stop screw. DO NOT over adjust.
e. If rpm continues to be fast, perform Key On Engine Off (KOEO) Self-Test.
- If Throttle Position (TP) sensor Diagnostic Trouble Code (DTC) is within range, remove tape from throttle body and check for other possible causes.
- If TP sensor DTC is out of range, adjust screw for proper TP sensor code. Lever must be in contact with the screw.
- If rpm is still fast, terminate the procedure and check for other possible causes.
f. If rpm drops to 600 rpm or lower, or the engine stalls, turn engine Off, 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 (Refer to PROCEDURES FOR PLUG INSTALLATION, below).
h. Reconnect the air cleaner hose. Start the engine, and check the idle rpm using a tachometer. Turn the plate stop screw clockwise to 600 +/- 25 rpm.
NOTE: DO NOT turn the plate stop screw counterclockwise. This may cause the throttle plate to stick at idle.
STEP 7
Turn engine Off and repeat Steps 4, 5, and 6.
STEP 8
Turn engine Off, and disconnect the negative battery terminal for at least 10 minutes.
STEP 9
Reconnect the Idle Air Control-Bypass Air (IAC-BPA) solenoid. Verify the throttle plate is not stuck in the bore, and the linkage is not preventing throttle from closing.
STEP 10
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. If idle problem still persists, look for other possible causes.
STEP 11
Run the KOEO Self-Test for proper TP sensor DTC.
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 (F0PZ-9F652-A).
STEP 3
Starting with the largest diameter gauge peg, attempt to insert through the throttle plate orifice.
STEP 4
- If the gauge peg goes through the orifice, use the corresponding color plug.
- If the 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.