Curb Idle Speed Adjustment
- On 4.9L, 5.0L and 5.8L engines, with engine off, install feeler gauge between throttle plate stop screw and throttle lever.On 4.9 use .050" feeler gauge. On 5.0L with automatic transmission use .050" feeler gauge. On 5.0L with manual transmission use .030" feeler gauge. On 5.8L with either transmission use .030" feeler gauge.
- On 2.3L, 4.9L, 5.0L and 5.8L engines, unplug spout in-line connector (Yellow/Light Green wire) near distributor and verify ignition base timing is correct. Timing is base ±2 degrees BTDC (refer to decal). On all engines disconnect idle speed control air by-pass solenoid. On 2.3L, 2.9L, 3.0L, 4.0L and 7.5L place transmission in Park or Neutral, run engine at 2500 RPM for 30 seconds.
- On 4.9L, 5.0L and 5.8L, place transmission in Park or Neutral and let engine idle for 2 minutes.
- On all engines except 3.0L, place automatic transmissions in Park and manual transmissions in Neutral. On 3.0L, place transmission in Drive. On 2.3L, 2.9L, 3.0L and 4.0L engines, check/adjust idle RPM, see IDLE RPM SPECIFICATIONS table, to adjust turn throttle plate stop screw. On 4.9L, 5.0L and 5.8L, check idle RPM, see IDLE RPM SPECIFICATIONS table. If an adjustment is necessary, turn off engine. Make an estimated adjustment of the throttle stop screw. Start engine repeat steps 3 and 4 until the idle is within specifications
- On 2.9L, 3.0L and 4.0L engines, shut engine off and repeat the following steps:
- Place transmission in Neutral or Park.
- Run engine at 2500 RPM for 30 seconds.
- On 2.9L and 4.0L engines, place automatic transmission in Park and manual transmission in Neutral.
- On 3.0L engine, place transmission in Drive.
- Check/adjust idle RPM.
- On 2.9L, 3.0L, 4.0L, 4.9L, 5.0L and 5.8L engines, disconnect battery for a minimum of 5 minutes. On 4.9L, 5.0L and 5.8L engines, remove feeler gauge from throttle plate stop screw and pad. On 2.3L, 4.9L, 5.0L and 5.8L engines, reconnect spout in-line connector (Yellow/Light Green wire).
- On all engines, with engine off, reconnect idle speed control air by-pass solenoid. Verify throttle is not sticking and linkage is not binding. Start engine and stabilize for 2 minutes then accelerate engine and allow to return to idle. Lightly depress and release accelerator. Let engine idle. On 3.0L idle speed should be 800-850 RPM with manual transmission and 670-770 RPM with automatic transmission.
- On 5.0 with automatic overdrive transmission check TV pressure adjustment.
NOTE:
On 4.9L, 5.0L and 5.8L a condition may occur where the engine may oscillate. This can be caused by the throttle plates being open enough to allow canister purge flow. To verify this condition, disconnect and plug carbon canister purge line. If purge is present, the throttle plates must be closed until the purge-induced idle oscillations stop.
IDLE RPM SPECIFICATIONS
| Engine | Idle RPM | |
|---|---|---|
| 2.3L | 550-600 | |
| 2.9L | 700-750 | |
| 3.0L | ||
| A/T | 600-650 | |
| M/T | 700-750 | |
| 4.0L | 675 | |
| 4.9L | ||
| C6 & E4OD | 650-700 | |
| M/T | 675-725 | |
| 5.0L | ||
| A/T | 675-725 | |
| M/T | 700-750 | |
| 5.8L | ||
| C6 | 780-830 | |
| E4OD | 730-780 | |
| M/T | 730-780 | |
| 7.5L | ||
| C6 & E4OD | 650-700 | |
| M/T | 650-675 | |