1. Autos
Send to a Friend via Email

Your suggestion is on its way!

An email with a link to:

http://autorepair.about.com/od/enginetroubleshootin1/a/TS_idle-speed.htm

was emailed to:

Thanks for sharing About.com with others!

You can opt-out at any time. Please refer to our privacy policy for contact information.

Troubleshooting Problems With Engine Idle

Help With Idling Issues Like Low Idle, Fast Idle, Bad Idle and Others

By

Troubleshooting Problems With Engine Idle
Ernesto Andrade/Flickr
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 (grandpa), 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.

Symptom: The engine will not idle smoothly, or it stalls during idle when the engine is warm. When the engine is warm or hot 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 (gramps), 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. 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. Idle speed set incorrectly.
    The Fix: Set idle speed to specs.
  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. The EGR valve may be bad.
    The Fix: Replace EGR valve.
  8. The engine may have mechanical problems.
    The Fix: Check compression to determine engine condition.
  9. The fuel injectors may be dirty.
    The Fix: Clean or replace fuel injectors.

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.

Symptom: Car stalls when stopped quickly. You are driving along and everything is just fine ... until you let off the gas pedal and apply the brakes. The engine starts shaking and may even stall. Not a good thing to happen because you lose power steering when the engine dies.

Possible causes:

  1. There may be a serious vacuum leak.
    The Fix: Check and replace vacuum lines as required.
  2. 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)
  3. Broken linkage.
    The Fix: Repair or replace as required.
  1. About.com
  2. Autos
  3. Auto Repair
  4. Troubleshooting
  5. Engine Troubleshooting
  6. Troubleshooting Problems With Engine Idle

©2014 About.com. All rights reserved.