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Old 07-23-2012, 07:34 PM   #1
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Default IAT sensor bad?

I have a 90 Miata, 1.8 turbo swap running on MSPNP Gen 1, GM IAT sensor from DIYautotune. This seems applicable to any MS though so I'll ask it here.

My IAT readings are way off, it started the other day on the highway I was seeing an IAT reading of 200F. Now when I hook up the computer and turn the ignition on (engine not running) the IAT reading is 214F instead of ambient. It stays around that while running and driving.

When I unplug the sensor the reading goes to 0F.

I unplugged the connector from the sensor and put a resistor across the two wires (3ohm resistor I think, leftover from trying to defeat the airbag light) and the temp went to 435F on the display. Which makes sense since the GM IAT sensor reads a higher temp at lower resistance.

Does this sound like a bad IAT sensor or something with the MS?
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Old 07-23-2012, 07:42 PM   #2
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Measure the IAT sensor resistance at normal, outdoor-ish temp and compare to the table. That should tell you.
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Old 07-23-2012, 07:45 PM   #3
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Good idea, I can't believe I didn't think of doing that.
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Old 07-23-2012, 07:50 PM   #4
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Yep, resistance at the current outdoor temp (~85) is 170, spec at 87F should be 1930 ohms. Looks like it is bad.
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Old 07-23-2012, 08:27 PM   #5
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Just measured mine to verify and at ~75F it's at 2600Ohms. You'll need a new one.
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Old 07-23-2012, 08:58 PM   #6
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Cool, thanks for the help.
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Old 07-23-2012, 10:00 PM   #7
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Mine started doing the same thing a little while back. Replaced it and life is good.
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Old 07-24-2012, 12:02 AM   #8
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I was surprised it went bad already...there is only about 2-3k miles on the sensor.
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Old 07-26-2012, 05:47 PM   #9
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I got the new sensor in today and everything works as it should again.
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