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Thread: 94 4Runner stalls at operating temp

  1. #1

    Default 94 4Runner stalls at operating temp

    94 4Runner, 260,000 miles, starts fine then stalls at operating temp. The Haynes Manual (#92075) says that engine RPM should not drop when the engine is warmed-up and the idle speed adjusting screw is turned all the way in. Is that correct?

    When I turn this screw all the way in, the engine would stall if I let it. I assume that the air valve is faulty (?). Or there is a vacuum leak.

    Two immediate questions - 1) Is the air valve part of the throttle body, or a separate unit that can replaced or cleaned; and 2) The chart, Fig. 17.2 on page 4-14 of the Manual (#92075), shows the vacuum - no vacuum by port (A,E,R, and P), but I can't find a diagram showing which vacuum hose is which.

    I really need some help because the dealer doesn't seem to care (I guess because its an older model), and I drive this vehicle everyday.

    Thanks!

  2. #2
    Join Date
    Jan 2007
    Posts
    4,850

    Default

    Hi Tom,

    It appears as if something has been lost in translation between Japanese and English and it was passed onto us. In the Toyota factory service manual it says "After warm-up - When the idle speed adjusting screw is turned in, the engine speed should drop below idle speed stop." Doesn't make sense grammatically, but I think there should be a "then" below stop. That would make sense, because of how the air valve operates. There are two bypass channels around the throttle plate - the air screw and the air valve. When cold, the wax-pellet type thermostat in the air valve holds the valve open to bypass the throttle plate, so the air screw has less of an effect on idle speed. As the engine warms up, the thermostat in the valve closes, so the air screw would have a much greater effect and would indeed cause the engine to stall when screwed in all the way.

    Now get a pen and your manual, because we're going to amend the chart in illustration 17.2. On your model year the test speed should be raised to 3500 rpm, there is no port A, and there should be vacuum at all three ports at 3500 rpm. From front-to-rear the ports are arranged R, E, P (but in your case it really doesn't matter because they all should perform the same).

    I believe the air valve is available separately, but based on the way the valve works, I don't think that's the cause of stalling. I would start by making sure the throttle body is clean (especially the passage that the air screw controls).

  3. #3

    Default

    Thanks for the reply! That clarifies a few things.

    The dealer, supposedly, cleaned the throttle body but the problem still occurs. After a series of restart/stall sequences (10 to 30 times), the engine runs fine until it cools-off. Since this seems temp related, I'm going to replace the coolant temp sensor then move on to check the throttle position sensor and from there, ... ?.

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