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Discussion Starter · #1 ·
In trying to troubleshoot an IACV problem (, I spent a huge amount of time trying to figure out how it works and how to test it. I am hoping to collect some info for a possible sticky thread to make this process easier for others. My info here is based on a 2002 GT-S.

The service manuals posted on the site ( have some information on testing (Manual Part 1, page DI-109 (page 320 in Adobe Reader) & Part 2, page SF-40 (page 177)), but it is geared to determining if the IACV is actually the issue, refers to Toyota SSTs, and shows the IACV in a wiring diagram as a black box. I'd like to provide something more practical for the average person doing this at home.

I will use Toyota's numbering system for the three IACV pins, starting with pin 3 at the top (when looking at the IACV mounted on the bottom on the throttle body) - this connects to the white wire with black stripes on the female connector on the wiring harness (the black wire with white stripes connects to pin 1 on the bottom, just to add to the confusion).

Here's where I need some help. The measurements below are on an IACV that may not be functioning correctly, so I am hoping someone without IACV / idle issues can reproduce the testing here, and see if a good IACV gives the same results (which will also tell me if mine needs to be replaced).
I found it was easiest to remove the intake air box to give me lots of clearance to do the testing.

The first thing I found really threw me off: When I tested resistance between the pins on the IACV with a digital meter, I got open readings between all combination of pins, regardless of the polarity of the test leads. I verified this using another meter, and got the same results. I also checked to see if any of the pins had a connection to the throttle body (should be equivalent to ground), which they did not (this was a suggestion I found on a Honda forum).

I then tried the testing using the "diode check" setting of my meters, and was able to get readings. This is odd, as you can typically check resistance on a diode, but it may have something to do with the battery voltage in the meter that is used when checking resistance. Results were as follows, using pin number, with the test lead colour (red or black) following in brackets. N/C indicates No Connection, or open (no reading). The second reading (in brackets) is using another meter (could be just a weak battery in one meter).

  • 1(R) - 2(B): 0.693 (668)
  • 1(B) - 2(R): N/C
  • 1(R) - 3(B): N/C
  • 1(B) - 3(R): N/C
  • 2(R) - 3(B): 1.96 (1605)
  • 2(B) - 3(R): 0.575 (531)
The second test I performed (again, as seen on another site) was to check the operation of the IACV using a 9V battery. This should produce a quiet "click" noise as the valve rotates, if it is functional (Please note: this will likely not work if your IACV is stuck open or closed because of fouling - all these tests were performed after my IACV had been removed and thoroughly cleaned). I did the same tests as above, reversing the positive and negative terminals for each pair of pins. The only test that produced a "click" result was with the negative terminal on pin 3, and the positive terminal on pin 2.
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