Seems kind of high, even though it does eventually drop back down to 1000 rpm after a few seconds.

Warm or cold makes no difference.

137 k miles.

What could be the cause?

1 Answer 1


You could have a defective brake booster.

Your brake booster assists vehicle braking by using engine vacuum to force a diaphragm to press the brake master cylinder shaft. If the diaphragm has a crack, engine vacuum can leak from the brake booster when you press the brake pedal.

This causes an excessive amount of air to leak into the engine intake, which can alter the idle speed.

The easiest way to test this theory is to pinch the vacuum line that supplies the brake booster. You can do this without damage by clamping the vacuum line between two coins with vise grip pliers or a C-clamp. (Coins will prevent damage to the rubber line.)

If you step on the brake with the engine running while the vacuum line is clamped and the idle speed no longer rises, you have a bad brake booster. You may also find that the idle speed without pressing the brake drops to a lower (now correct) rpm.

Don't drive while the vacuum line is clamped; it would be very hard to stop without power brakes.

  • What's normal idle rpm? Manual or automatic?
    – F Dryer
    Commented May 10 at 17:40

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