Intake Air Temp Sensor Bad?

[g_wilson]

My IAT sensor is not functioning properly, 75 degrees with engine cold (not running) when the outside temp is 45. Coolant temp is close to outside temp. Start the engine and it goes to about 85 degrees and stays there regardless of the outside temperature. No codes, just not accurate.

Looks like I need a new one? How much does this effect a stock engine with a TT chip? Can I pick one up at the local autoparts store?

Thanks,
Greg

 

[unix_punk]

Don't know for sure if its readily available, but what happens to the temp when its unplugged? Ever go past 85?

 

[russgoodman]

If you end up needing one, my buddy got one off Mike at Full Throttle the other day, like $17 or so. Just FYI.

 

[salvageV6]

Take it out, disconnect the wiring, and test it with an ohmmeter and clip leads.

At room temperature 70 degrees optimum, it should read 3400 ohms.

In a pan of hot almost boiling water, 210 degrees optimum, (don't melt it), it should read lower ohms at about 185 ohms, 160 degrees would read 450 ohms.

In the freezer at about 0 degrees it should read 25,000 ohms higher resistance, 20 degrees it should read 13,500 ohms.

Assuming a stock MAT, manifold air temperature sensor.

 

[Turbo6Smackdown]

Gotta bring this back-wanna know how this all works. Ohmmeter. What setting. 2000k 200k 20k 2000 or 200? Which terminal does the red lead go on? I tried every way possible, and got 1, or like 2.4 something. And what's a manifold air temperature sensor. I've never seen that on our cars before.

 

[earlbrown]

There is not manifold air temp sensor. Only the temp sensor on the MAF area. After the intercooler the ECM has no idea on the temp.

 

[Raeban]

Intake Air Temp Sensor, Manifold Air Temp Sensor and Air-charge Temp Sensor are names that are often interchanged for a sensor that has the same purpose, to measure the temperature of the air entering the engine. On a turbo car, our intake manifold temps can be quite a bit different than the air inlet temps but even still the factory manual refers to our only air temperature sensor as a Manifold Air Temp Sensor. Additionally, guys running a speed density tune like to mount their air temperature sensor to the manifold to read the air temperature after the turbocharger.

Here is the factory test chart as well. The scale on your multimeter needs to be set to the next highest scale to read the desired value if it doesn't auto-range.

 

[Turbo6Smackdown]

Sweet. Thank you. My sensors both read 003 when I ohm them out. Somethin' ain't right. How do I check my ohmmeter.

 

[Raeban]

Sweet. Thank you. My sensors both read 003 when I ohm them out. Somethin' ain't right. How do I check my ohmmeter.

Are you sure you are reading the multimeter correctly?

On multimeters that don't autoscale you have to select the right range. I will try to give an example:

It's 85F outside. This value isn't on the chart but falls between 1600 ohms and 3400 ohms, and without doing the math lets say for this example I should see 2080 ohms.

If I measure the resistance here is what I should get:

Scale-------Value
200---------1 The reason is because the meter will only read up to 200 ohms and I should be getting 2080 ohms so I am off the scale
2000-------1 Same reason as above
20K-------- 2.08 This scale will read up to 20,000 ohms but you need to multiply your result by 1000
200K-------2.1 This scale will read up to 200,000 ohms, in the case of the cheap meters it will round your result, again multiply by 1000
2000K------002 This scale reads so large that you don't get the decimal value at all, but if you multiply by 100,000, it will give you a result of 2000 ohms (which is cropped)

All that said, it sounds like you were using a meter to measure your sensors on the 2000K scale and getting a cropped value of 3000 ohms. Retest on the appropriate scale for the resistance you intend to see.

 

[Turbo6Smackdown]

Yes. I misread your original post and seen "set on highest scale". sorry. So on the above options, is there an option that doesn't require (not that I suck in math whatsoever, but it just seems like it's missing something) all sorts of math and what not? A scale that doesn't move a decimal point, round off, truncate, or otherwise require additional steps? The above options seem like something only close enough, and not totally correct. Which is not really a good thing in electronics lol. None of them seem like they belong to me.

 

[Turbo6Smackdown]

Ok, got it. 3.01 and slowly and steadily declines. 3.00 2.99, 2.98, 2.97 and it won't stop. Both sensors.

Now the new sensor starts at 2.32 and steadily declines. It's a different reading each time lol.

 

[Raeban]

Assuming that was on the 20K scale you are looking at 2970 to 3000 ohms. What temp are you testing at? And in regards to your earlier post, add an auto-ranging multimeter to your wish list. If you don't want to spend a bunch of cash I like this one because of the inductive DC ammeter feature (nice for running down dead battery issues)

http://www.amazon.com/MASTECH-MS2108A-Ranging-Backlight-Protection/dp/B008MV2AHU/ref=sr_1_2?s=hi&ie=UTF8&qid=1408803954&sr=1-2&keywords=mastech ms2108a

 

[Turbo6Smackdown]

I like that. I have auto electrics class starting Monday so I may need one of those. I'm testing at room temperature. Which is about 68 in here. The readings won't settle down.

 

[Raeban]

I wouldn't be too worried about the readings dropping some. The ohmmeter works by applying a small voltage across the resistor so the result you are getting is likely due to some heating from the testing.

 

[Turbo6Smackdown]

So should I be taking the first reading that comes up on the screen? Or is that the sign of an old battery. Because these readings aren't recovering. I come back from watching them drop to say 2.45 after like ten minutes, and they start right back up at 2.45 and continue to drop. How does that happen?

By the way, thanks for going out of your way and explaining shit to me. I appreciate it.

 

[Raeban]

I would just take the first reading as that is the common way of taking the measurement.

 

[Turbo6Smackdown]

Roger.

 

[earlbrown]

it sounds like your meter might be putting heat into the sensor. When on the Ohms scale it sends a small current through what you're testing.

throw your IAT in the refrigerator and/or freezer and see what it reads. Or set it outside (in the shade) for a while and probe it again.

 

[Turbo6Smackdown]

No heat's getting into the sensor BUT, I like fridge idea. Trying it now.

 

[Turbo6Smackdown]

Stuck it in the freezer for 10 minutes. Ohmed out 1298 and started to drop very rapidly...1298 equals roughly 113 and when it drops that's approaching 130 degrees. Coming out of the FREEZER? How does my sensor do the exact opposite of resistance theory lol.