Manual/C6

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.

Service Decal Location (Typical Throttle Body):

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-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.

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. 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
Turn Off the engine and 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 0.050" - A/T (0.030" - M/T) feeler gauge between the throttle plate stop screw and the throttle lever.

STEP 6
Disconnect Idle Air Control (IAC) 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 # F0PZ-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 +/- 25 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), otherwise proceed with next step.
d. Restart engine and check idle speed, using a tachometer.
NOTE: For vehicles with Mass Air applications, 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
Remove the feeler gauge from throttle plate stop screw and lever pad.

STEP 11
Shut Off engine and disconnect battery for at least 10 minutes.

STEP 12
Reconnect the in-line SPOUT connector.

STEP 13
Reconnect the IAC solenoid. Verify that the throttle is not sticking in the bore, and the linkage is not preventing the throttle from closing.

STEP 14
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 exists, check for other possible causes.

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 15
Perform Key On Engine Off (KOEO) self test for proper Throttle Position (TP) sensor Diagnostic Trouble Code (DTC).

STEP 16
On Automatic Overdrive (AOD) Transmission applications, check TV pressure adjustment.