How To Test And Adjust The Idle Switch (1993-1995 3.0L V6 Nissan Quest)

The throttle position sensor on the 1993-1995 3.0L V6 Nissan Quest or Mercury Villager is two components in one assembly. One part is the throttle position sensor and the other is an idle switch.

In this tutorial, I'm going to show you how to check whether the idle switch is working correctly and how to adjust it if it's misadjusted or if you've replaced the TPS/idle switch assembly.

Both the idle switch test and adjustment can be done with a multimeter, and I'll walk you through both procedures step by step.

NOTE: In the Nissan service literature, the idle switch is referred to as the Closed Throttle Position Switch. For simplicity's sake, I'll just be calling it the idle switch.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L V6 Nissan Quest: 1993, 1994, 1995.
• 3.0L V6 Mercury Villager: 1993, 1994, 1995.

TPS SENSOR DIAGNOSTIC TESTS:

• How To Test The TPS With A Multimeter (1993-1995 3.0L V6 Nissan Quest).

TPS/IDLE SWITCH CIRCUIT DIAGRAM:

• TPS And Idle Switch Circuit Wiring Diagram (1993-1995 3.0L V6 Nissan Quest).

Idle Switch Continuity Tests

Your Nissan Quest or Mercury Villager's idle switch has only one job, and that's to inform the powertrain control module (PCM) when the throttle plate is fully closed and when it's at wide open throttle (WOT). It does this by opening and closing specific internal circuits, depending on the throttle plate's position.

Since the idle switch is basically an ON/OFF switch, testing it is pretty easy. All we have to do is check continuity (with a multimeter) between specific terminals with the throttle plate in two positions:

• Closed throttle, and
• Wide open throttle.

To get started, the throttle position sensor (TPS) assembly itself, on your 1993-1995 3.0L V6 Nissan Quest or Mercury Villager, has two separate connectors. Specifically:

• One connector has three wires going into it. This connector belongs to the throttle position sensor (TPS) portion of the assembly.
• The second connector is part of the TPS assembly itself. This connector and its three terminals belong to the idle switch portion of the assembly.

Using the illustration above, the idle switch terminals we'll be testing are labeled 1, 2, and 3.

NOTE: All continuity checks are performed directly on the male spade terminals of the idle switch, not on the engine wiring harness connector that connects to them.

Idle Switch Closed Throttle Specifications
Throttle Angle	Pins	Ohms
Closed Throttle	2 and 3	Continuity
Open Throttle	2 and 3	No Continuity

Idle Switch Wide Open Throttle Specifications
Throttle Angle	Pins	Ohms
Closed Throttle	1 and 2	No Continuity
Open Throttle	1 and 2	Continuity

If the throttle switch on your Nissan Quest (Mercury Villager) doesn't pass any of the above pin continuity tests, then, before replacing it, you need to make sure that it's not misadjusted. The next subheading will help you with this procedure.

Adjusting The Throttle Position Sensor Assembly

The throttle position sensor (TPS) assembly needs to be adjusted any time it's replaced, or if testing shows that the idle switch's closed-throttle or wide-open-throttle continuity is out of specification. The good news is that this adjustment is very straightforward and easy to do.

NOTE: For this adjustment to work correctly, the TPS assembly must be fully connected to its electrical connectors during steps 1 through 6.

Here's what you'll need to do to properly adjust the TPS assembly:

1. Turn the ignition switch to its OFF position and make sure the TP sensor assembly is connected to its connectors.
2. Turn the ignition switch to its ON position but don't start the engine.
3. Place your multimeter in Volts DC mode and:
   • Connect the red multimeter test lead to the RED wire that connects to the pin labeled with the number 5 (see the illustration above). This is the RED wire of the engine wiring harness TPS connector.
     • You'll need to use a back probe on the connector or a wire piercing probe on the RED wire to connect your multimeter test lead to this circuit.
     • NOTE: The TPS/idle switch sensor assembly must be connected to both of its connectors.
   • Ground the black multimeter test lead on the battery negative (-) terminal.
4. Adjust the TPS sensor by rotating it until the output voltage is within specification:
   • Specification: 0.45 to 0.55 Volts DC.
5. Once the output voltage has reached the above voltage specification, tighten the TP sensor assembly mounting bolts.
6. Recheck the output voltage to make sure the TP sensor didn't move on you when you tightened the two bolts.
7. Now, disconnect the TPS from its two connectors and with your multimeter in Ohms mode check that:
   • Idle switch pins 1 and 2 have continuity at closed throttle plate position.
   • Idle switch pins 2 and 3 have continuity at wide open throttle plate position.
8. If both the voltage spec and the continuity specs are present, the TPS assembly is correctly adjusted.

Where To Buy Your TPS/Idle Switch Sensor And Save

Where can you buy the TP sensor for your 3.0L Nissan Quest? You can buy it at your local auto parts store, but it's gonna' cost a whole lot more. I suggest taking a look at the price of the TP sensor in the following links and compare:

Not sure if the above TP sensor fits your particular 3.0L Nissan Quest or Mercury Villager? Don't worry, once you get to the site, they'll make sure it fits by asking you the particulars of your vehicle. If it doesn't fit, they'll find you the right one.

More 3.0L V6 Nissan Quest Diagnostic Test Tutorials

You can find a complete list of diagnostic tutorials and wiring diagrams in this index:

• 3.0L V6 Nissan Quest Index Of Articles.

Here's a small sample of the tutorials you'll find in the index:

• How To Test The Fuel Pump (1993-1998 3.0L V6 Nissan Quest).
• How To Troubleshoot A Cylinder Misfire (1993-1998 3.0L V6 Nissan Quest).
• How To Test For A Blown Head Gasket (1993-1998 3.0L V6 Nissan Quest).
• How To Test The Fuel Injectors (1993-1995 3.0L V6 Nissan Quest).