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Toyota 4Runner Idle Speed Problems?

Q. Problem: The car idles at about 1,500 RPM for a while. During this time it sounds like its revving a lot higher than that, it sounds like a fan is blowing air really fast. This only lasts for a while, or until the car hits about 3,000 rpm, by pushing the accelerator, at which point it returns to about 800 rpm, dies down on its own eventually, and will stay that way until shut off.

Toyota 4Runner Idle Speed Problems?

If left off for about ten minutes it will repeat this. However, if turned on again after about four minutes it will idle normally at about 800 rpm without the loud sound of air. It's been doing this for years now. Its not debilitating, I just think it wastes gas, and if it's caused by something, like the oxygen sensor, it could effect other things too. I don't know if you would know how many kpg we should be getting per tank, 50 liters, but we're only getting about 350 kilometers city driving.

  • 1994 Toyota 4Runner 4x4
  • 3.0 liter SOHC V-6
  • Manual transmission
  • 122,000 kilometers
  • Fuel Injection
  • Rear ABS brakes
  • P/S and cruse control

Thanks a lot for the help, if you can give me any.


From what you're describing Brendan, it sounds like the normal operation of the truck. When the engine is cold and first started, the idle will be high until the engine warms up. Since this vehicle is fuel injected, the idle will start high and gradually decrease as the engine warms.

The Auxiliary Air Valve, mounted under the throttle body, raises the idle speed when the engine is cold. Controlled by a thermowax plunger type valve, When the engine coolant is cold, the thermowax contracts the plunger which opens the valve allowing air to bypass the throttle plate and idle adjusting screw into the intake manifold. When the engine coolant warms up, the valve closes and the bypass air flow is blocked.

Toyota 4Runner Idle Speed Problems?
Toyota Auxiliary Air Valve

The "roar" that is heard is the cooling fan clutch. The thermal viscous fan drive is a silicone-fluid-filled coupling used to connect the fan blades to the water pump shaft. The coupling allows the fan to be driven in a normal manner. This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher engine speeds.

A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit (a typical viscous unit is shown in. This spring coil reacts to the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a certain point. Until additional engine cooling is necessary, the fan will remain at a reduced rpm regardless of engine speed.

Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the radiator core causes a reaction to the bimetallic coil. It then increases fan speed to provide the necessary additional engine cooling.

Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the fan speed is reduced to the previous disengaged speed.

As for the fuel economy, by my calculations, using the figures you gave me, you are getting about 16.4 miles per gallon city which is pretty good for that truck.

Toyota 4Runner Idle Speed Problems?
Typical Cooling Fan Clutch

Additional Information provided courtesy of ALLDATA

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© 2003 Vincent T. Ciulla

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