The engine idles too fast

Symptom: The engine idles too fast. After the engine has run long enough to be warm, the idle speed does not come down to normal. You really notice it when you come to a stop and must have to push hard on the brake pedal to keep the car from moving.

Possible causes:

1. If you have a carburetor, you may have a bad accelerator pump or power circuit.

The Fix: Replace accelerator pump or replace carburetor.

2. The engine may be overheating.

The Fix: Check and repair cooling system.

3. The fuel pressure regulator may be operating at too low a pressure.

The Fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)

4. The ignition timing may be set wrong.

The Fix: Adjust ignition timing.

5. There may be some type of ignition problem.

The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.

6. There may be a fault in the computerized engine control system.

The Fix: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)

7. There may be a vacuum leak.

The Fix: Check and replace vacuum lines as required.

8. You have a bad idle speed control unit.

The Fix: Replace idle speed control unit.

9. The alternator may not be working properly.

The Fix: Replace alternator.

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Problems With Engine Idle


Troubleshooting Problems With Engine Idle

In many ways, engine idle is a good measure of your engine’s health. If anything is going wrong under the hood, there’s a good chance it will be affecting your car’s idle speed and quality. Problems with idle speed, things like slow idle, low idle, bad idle, lumpy idle, fast idle — these are symptoms that should be investigated, troubleshooted, diagnosed and repaired. The following symptoms and related problems should act as a guide in helping you troubleshoot your idle issues.

Symptom: The engine will not idle smoothly, or it stalls during idle when the engine is cold. When the engine is cold and you take your foot off the gas pedal, the engine runs very rough and may even stall. When you run the engine at higher speeds, it seems to run fine.

Possible causes:

1. If you have a carburetor, you may have a bad accelerator pump or power circuit.

The Fix: Replace accelerator pump or replace carburetor.

2. There may be a vacuum leak.

The Fix: Check and replace vacuum lines as required.

3. There may be some type of ignition problem.

The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.

4. The ignition timing may be set wrong.

The Fix: Adjust ignition timing.

5. There may be a fault in the computerized engine control system.

The Fix: Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)

6. The EGR valve may be bad.

The Fix: Replace EGR valve.

7. The engine may have mechanical problems.

The Fix: Check compression to determine engine condition.

8. Idle speed set incorrectly.

The Fix: Set idle speed to specs.

9. The fuel injectors may be dirty.

The Fix: Clean or replace fuel injectors.