Idle Switch Adjustment for 85-92 Vanagon.

Proper Idle Switch Adjustment

Many folks call me with the complaint that their Vanagon is not idling properly. Either they are idling too high or too low (stalling) or the idle isn’t steady. There can be several factors that contribute to this problem however most of the time the culprit is an out of adjustment idle switch on the throttle body. This switch is located below the throttle body on 85-92 Vanagons and most folks don’t even know that it exists. However if the computer is looking for a signal from it and is not seeing it, then it thinks it that the van is still driving down the road and not sitting at the light. I am going to give instructions for inspecting and adjusting this switch for 85-92 Vanagons.

Go to the rear of the van with the engine not running. Remove the engine lid and set it aside. At around the middle of the engine compartment you will see the throttle body attached to the metal air distributor for the intake. Use your fingers to move the throttle arm on the top of the throttle body from where it is at rest (idle position) to the full throttle position (as far as you can move it). Right when you are getting to the full throttle position you should hear a small “click” noise. Now slowly move the throttle arm back to idle position. Right before you get to this position you should hear the same small click. If you don’t hear it then the switch is out of adjustment. If you hear it then test the switch for continuity with a multimeter. It should have zero resistance at idle and full throttle position. If it doesn’t then you need a new one.

If you need to adjust the switch, the correct, Bentley way to do this is from above with a small allen tool. If you look straight down at the throttle body from above you will see a small metal plate with two allow screws in it. One of them is in a slot and the other is to the left of the slot. You want to use your allen tool to unlock the screw that is in the slot. Not use the same allen tool to turn the other screw to the left. You will see that as you turn it just slightly one way to the other the screw that is in the slot will move to the right or to the left. Usually, if your switch is out of adjustment, and you turn the screw so that the one in the slot moves to the left a bit, you will get to a point where you will hear a small clicking noise. Move it back and forth a few times until you get a consistent point where you can hear the clicking and then lock the screw that is in the slot at that point. Now move the throttle again several times from full throttle back to idle by hand. You should hear the click when at the idle position now. If not loosen the screw in the slot again and move it just a little more to the left and try again. What you are looking for is for the switch to click right at the idle position. You don’t want to adjust it too much so that it clicks before idle because then you will have a hesitation when taking off. This is the way to do it if everything is still in good condition.

However in the real world, many times you deal with the problem of someone messing with this switch before you, stripping out the allen head screws so that they are frozen and you can’t adjust them. Or they are just so corroded that they are melted and there is nothing for the tool to grab on to. If this is the case then you have to go to Plan B.

Plan B involves removing the intake boot and the two phillips head screws that hold the throttle body to the intake. Flip the throttle body upside down. Now you should see a black plastic cover that goes over the switch. Pull it off and set it aside. You will see the metal arm of the switch that rides up against the plastic cam that actuates the switch. The end of the arm is in the shape of a “U”. Use a pair of needle nose pliers and tweak the very end of the arm. You want to bend the part of the “U” that touches against the cam so that the “U” is just a little bit wider than it was (not a bunch, just a tweak). Now flip the switch over and try the test again. Tweak the “U” until the switch works properly at idle position. Now put everything back together and start the van. It should idle properly at around 950 rpms.

If you try to adjust your switch and it doesn’t click at all no matter what you do to it, most likely your switch itself is bad and needs to be replaced. You can also check it with an ohm meter to see if it is actually working electrically. You want to see “open” or infinite resistance when the switch is off idle and “closed” or very low resistance when the switch clicks at idle position and at full throttle position. To know what I am talking about, set your meter to ohms and just hold the two test leads apart. That is “open” so what ever your meter is reading at that point is what it should read at when the circuit is open. Now touch the two leads together. The meter may read zero or a very low resistance depending on how sensitive your meter is. That reading is what you should be looking for when the switch is closed or a very low ohm reading just above that. If it is reading hundreds or or thousands of ohms then the switch is bad. Do the readings a few times until you get some consistent readings.

Some folks try to work around idle control problems by raising the rpm or unplugging the idle stabilizer valve on the center of the engine. If you notice this valve unplugged, plug it back in. If the RPMS are still too high you might want to check your timing with a timing light. If the timing is on the money (7 degrees BTDC) then adjust your rpms down by turning the idle air screw (large slotted screw on the top of the throttle body) in a little. Count your turns so that you can put the screw back to where you had it originally if you find your real problem isn’t this screw.

If you are still having a problem with your idle after doing all of this then either your idle air stabilizer valve or the idle control unit is faulty. I would try cleaning the valve with carb cleaner and see if this helps. If not then swapping in a known good idle air valve or ISCU would be a great way to troubleshoot this problem. If known good ones aren’t available to borrow then you just need to flip a coin and decide which of these two expensive parts you want to try to replace first. Smell your ISCU (located behind the tail light on the passenger side on the 86-92 Vanagon). If it smells burnt then it probably is and needs to be replaced. I know they are expensive but having a properly functioning idle control circuit is important to keep your van running well, cut down on fuel usage, and keep the van from stalling when using the A/C or turning.

Idle Air Stabilizer Valve-
025906457AX
Idle Stabilizer Control Unit-
251907393D
Throttle Position Switch
025906011A

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