Manual/C6

NOTE: Curb and fast idle speeds are controlled by the Powertrain Control Module (PCM) and Idle Air Control (IAC) valve assembly. The IAC valve is not adjustable. A large increase or decrease in closed plate airflow from the calibrated level will not allow effective idle speed control.

Throttle Body Assembly Decal Location:

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 (TP 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 valve still applies.

REMEMBER
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:
- Battery and charging system integrity
- Contamination within the IAC component
- 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.)
- Exhaust system, EGR.

VERIFY
- Transmission is in Park (A/T), or Neutral (M/T)
- Parking brake is applied (automatic brake release 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 diagnostic trouble codes have been resolved.

IDLE SPEED CHECK PROCEDURE

STEP 1
Engine "Off", connect a tachometer according to manufacturer's instructions. Disconnect negative (-) terminal of the battery for 5 minutes, then reconnect.

STEP 2
Start engine and stabilize for two minutes, then goose (snap) the throttle and let it return to idle, lightly depress and release the accelerator and let engine idle.

STEP 3
If the engine does not idle properly, Shut "Off" engine and unplug SPOUT line connector.

STEP 4
Start engine, verify that ignition timing is at base +/- 2° BTDC, adjust if necessary. Shut "Off" engine.

STEP 5
Install .050" (A/T) / .030" (M/T) feeler gauge between throttle plate stop screw and the throttle lever.

STEP 6
STOP engine, and disconnect IAC solenoid.

STEP 7
Start and IDLE engine for 120 seconds.

STEP 8
Place the transmission in Park (A/T), or Neutral (M/T).

STEP 9
Use a tachometer and verify idle speed is at 675 +/-150 rpm (A/T), or 700 +/-150 (M/T).

RPM Too Low
Do not clean throttle body, check for throttle plate orifice plug.
- If no orifice plug present, turn throttle screw clockwise to 675 +/-25 rpm (A/T), or 700 +/-25 rpm (M/T).
- If an orifice plug is present from previous service, remove orifice plug, then adjust throttle 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 orifice in throttle plate with tape. If 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 Airflow applications, reconnect air intake duct hose before checking the rpm.
If the engine stalls, crack open the throttle plate stop screw, but 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 plate, and Refer to Diagnostic Routines check for possible causes.
- If TP sensor DTC is out of range, adjust screw for proper TP sensor code. Lever must be in contact with throttle screw.
- If rpm is still fast, terminate the procedure and check for Refer to Diagnostic Routines check for possible causes.
f. If rpm drops to 675 +/-150 rpm (A/T), or 700 +/-150 rpm (M/T) or below, or engine stalls, turn engine "Off", disconnect the air cleaner hose and remove tape from throttle plate.
g. Install orifice plug with proper color code depending on throttle plate orifice size (Refer to THROTTLE PLATE ORIFICE PLUG INSTALLATION, below).
h. Reconnect air cleaner hose. Start engine. Check idle rpm using tachometer. Turn throttle plate stop screw clockwise to 675 +/-150 rpm (A/T), or 700 +/-150 rpm (M/T).
NOTE: Do not turn the plate stop screw counterclockwise. This may cause the throttle plate to stick at idle.

STEP 9
Remove feeler gauge from throttle plate screw and throttle lever.

STEP 10
Shut engine "Off" and disconnect battery for a minimum of 10 minutes.

STEP 11
Reconnect SPOUT line.

STEP 12
Engine "Off", reconnect IAC solenoid. Verify throttle plate is not stuck in the bore and linkage is not preventing throttle from closing.

STEP 13
Start and idle engine for two minutes. Goose (snap) accelerator and return to idle. Lightly depress and release the accelerator, then let engine idle. If idle problem persists, Refer to Diagnostic Routines for possible causes.

STEP 14
Run KOEO Self-Test for proper TP sensor code output.

THROTTLE PLATE ORIFICE PLUG INSTALLATION

Throttle Body Assembly:

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

2. Select proper color plug by using the Go/No-Go gauge pegs, included with the service kit.

3. Start with largest diameter gauge peg and attempt to insert it through throttle plate orifice.

- If gauge peg goes through the orifice, use corresponding colored plug.
- If gauge peg does not go through, proceed with next smaller gauge peg for Go/No-Go Test.

NOTE: It is important that the largest Go/No-Go combination is used in determining the proper plug size.

4. If the smallest gauge peg does not go through the orifice, use reamer bit and handle included with service kit, to enlarge throttle plate orifice. Wipe bearing grease on both sides of the plate orifice and on reamer bit to hold the brass chips. After reaming, wipe throttle plate clean, then return to Step 3 to determine proper orifice plug size.

5. Use the installation tool from service kit, push plug into orifice until it bottoms out in throttle plate.

6. Open and snap shut the throttle several times to verify proper plug retention.

7. Reconnect air inlet tube(s).

8. Reset idle rpm per engine requirement, using throttle plate stop screw.