How to Test the Idle Switch of the TPS (1.6L Toyota Corolla -1.6L Geo Prizm)

In this tutorial I'm gonna' show you how to test the idle switch portion of the 1.6L Toyota Corolla throttle position sensor. You'll also find the instructions on how to adjust the idle switch/throttle position sensor assembly.

As you're already aware, the throttle position sensor on your 1.6L Toyota Corolla (1.6L Geo Prizm) is made up of the idle switch and the throttle position sensor. This is the reason why the TPS connector has 4 wires instead of the usual 3.

Here are the contents of this tutorial at a glance:

  1. Idle Switch Continuity Tests.
  2. Adjusting the Throttle Position Sensor Assembly.
  3. Location of the Throttle Opener Vacuum Diaphram.
  4. Location of the Throttle Stop Screw.
  5. Where to Buy Your TP Sensor and Save.

If you need to test the throttle position sensor part of the idle switch, this tutorial will help: How to Test the Throttle Position Sensor (1.6L Toyota Corolla).

Idle Switch Continuity Tests

How to Test the Idle Switch of the TPS (1.6L Toyota Corolla -1.6L Geo Prizm)

To find out if the idle switch is doing its job (or not), we're gonna' measure the continuity between 2 specific pins with a multimeter in Ohms mode.

The two TPS terminals that we need to locate/identify are terminal #2 and terminal #1 (using the illustration above).

IMPORTANT: If your 1.6L Corolla is a 1989 - 1992 year model, then the throttle body comes equipped with a Throttle Opener Diaphragm Assembly. You will need to apply vacuum to the Throttle Opener with a vacuum pump to perform the idle switch test (to see the location of the Throttle Opener: Location of the Throttle Opener Vacuum Diaphragm).

1. Turn off the ignition switch and disconnect the TPS from its engine wiring harness connector.

2. Insert the specified thickness feeler gauge between the throttle stop screw and throttle lever and check for the specific continuity shown in the table below (to see the location of where you need to place the feeler gauge: Location of the Throttle Stop Screw). If not within specification, adjust or replace the TPS assembly.

Idle Switch Continuity Specifications
Feeler Gauge Thick. Pins Ohms
.015 In. (.41 mm) 1 and 2 Continuity
.035 In. (.89 mm) 1 and 2 No Continuity

If the throttle switch on your 1.6L Toyota Corolla (1.6L Geo Prizm) 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

How to Adjust the TPS (1.6L Toyota Corolla -1.6L Geo Prizm)

If you need to remove and replace the throttle position sensor assembly... you'll need to adjust it to the correct specification before you bolt it down.

This is a pretty easy adjustment and in this section I'll show you how to do it.

NOTE: If your Corolla is equipped with a Throttle Opener Assembly, you'll need to apply vacuum to it with a vacuum pump while you adjust the TPS.

This is what you'll need to do:

  1. Turn the ignition switch to its Off position and make sure the TP sensor assembly is disconnected from its connector.
  2. Place your multimeter in Ohms mode.
  3. Place the .035 In. (.89 mm) feeler gauge between the throttle stop screw and the throttle lever and:
    1. Test continuity between terminal #1 and #2. Your multimeter should register NO CONTINUITY.
    2. If continuity exits, adjust the TPS sensor by rotating it until NO CONTINUITY exists.
    3. Slightly tighten the TPS screws.
  4. Place the .016 In. (.41 mm) feeler gauge between the throttle stop screw and the throttle lever and:
    1. Test continuity between terminal #1 and #2. Your multimeter should register Continuity.
    2. If continuity does not exist, adjust the TPS sensor by rotating it until continuity exists.
    3. Slightly tighten the TPS screws.
  5. Repeat steps 3 and 4 to verify No Continuity and Continuity exist with the indicated feeler gauge thickness.
  6. Once the proper continuity specs have been verified, tighten the TP sensor assembly mounting bolts.
  7. Once you're done, recheck the continuities once more to make sure the TP sensor didn't move on you when you tightened the two bolts.