DIY Fuel injection thread.

[gibbon]

I have a fast-reacting IAT probe here which I was going to replace the stock item on the rx7 with. Only problem is that it doesn't have a part number or anything on it (I thought it was Aeroflow brand but it doesn't seem to match their product visually). I understand that some of these probes are polarity sensitive, how do I work out if this one is, and if so, which pin is which?

[Rookie]

1 hour ago, gibbon said:

I have a fast-reacting IAT probe here which I was going to replace the stock item on the rx7 with. Only problem is that it doesn't have a part number or anything on it (I thought it was Aeroflow brand but it doesn't seem to match their product visually). I understand that some of these probes are polarity sensitive, how do I work out if this one is, and if so, which pin is which?

If it is 2 wire then without a doub it is a NTC sensor, so it is just a variable resistor, there is no polarity so no worries there, the calibration might be a different thing though, easy enough to figure out with an accurate thermometer and a decient ECU, just see what the analog voltage is at room temp, and then again at 100 °c and then a couple more points in between, it wont be linear. It should look something like the data for this bosch one.

https://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data Sheet_70129803_Temperature_Sensor_NTC_M12-L.pdf

[kpr]

as above  polarity doesn't matter.       wire to a  an-temp and sensor ground.  link has plenty of calibrations in drop down menu that covers most of them.  

main thing with iat sensors is to mount them somewhere to minimize heat soak.   a sensor that reads incorrect due to heat soak is worse than none at all. 

[gibbon]

7 hours ago, kpr said:

as above  polarity doesn't matter.       wire to a  an-temp and sensor ground.  link has plenty of calibrations in drop down menu that covers most of them.  

main thing with iat sensors is to mount them somewhere to minimize heat soak.   a sensor that reads incorrect due to heat soak is worse than none at all. 

ok. I was going to wire it to the original IAT harness as it's already there. presumably the calibration can be changed afterwards in the menu (come to think of it, considering I don't have a p/n for it I guess I'd better get some readings off it first)

Stock position is on the underside of the manifold which seems like a terrible place as far as heatsoak is concerned, I'll move it to the plastic pre-throttle body pipe

I'll take your guy's word for it that it's non polarity sensitive, but I did see a two wire aeroflow one that was, admittedly it didn't look too much like this one 

[kpr]

Yep if the stock one is 2 wire,  using same cables are fine as they will already be wired to said inputs.     

Can compare against the water temp sensor reading, when the car/engine is at ambient temp.  to double check the calibration.   

[ajg193]

On 28/04/2026 at 06:21, gibbon said:

ok. I was going to wire it to the original IAT harness as it's already there. presumably the calibration can be changed afterwards in the menu (come to think of it, considering I don't have a p/n for it I guess I'd better get some readings off it first)

Stock position is on the underside of the manifold which seems like a terrible place as far as heatsoak is concerned, I'll move it to the plastic pre-throttle body pipe

I'll take your guy's word for it that it's non polarity sensitive, but I did see a two wire aeroflow one that was, admittedly it didn't look too much like this one 

Position is critical, if you have it pre-throttlebody you will need to compensate with a lot of awkward blending with coolant temperature to estimate temperature of the air actually getting into cylinder. General consensus (except by toyota) seems to be that you want the sensor as close to the cylinder head as possible

[kpr]

he will have a hard time getting it close to the cylinder head on a rotary.    

But anyway, I'd rather have a sensor that reads falsely  low  than high.   Especially  if running in a modeled fuel equation, that does fuel trims in the background.    If iat reads low, engine runs a little bit richer.  if reads high will  pull too much fuel and run lean.  

No iat fuel correction,  engine runs richer when inlet temps are hot.  leaner when cold.    Not ideal, but better than the other way around