IAT Sensor Issues

[NVRL8]

I have had flaky IAT readings for years. I know the sensor is not really used for anything, but I want to go to speed density where the sensor becomes important. Today I turn the key on engine off and the IAT reading was 156 and dropped to 139. I started the car and there was a rapid drop to 44. With the car running the readings varied between 31-52. Outside temp is 60. When I unplug the sensor the readings are similar with no code thrown. Any ideas?

 

[mikestertwo]

The IAT is used to calculate fueling. If it is still reading a temp when it is unplugged then you have a short somewhere or the computer is bad.

 

[NVRL8]

Thanks for reply. Where should I start as far as diagnosing? Swap computer with known good?

 

[mikestertwo]

Thanks for reply. Where should I start as far as diagnosing? Swap computer with known good?

If you have a known good computer readily available then yes, swap it out. It's the easiest thing to try first. Also check for corrosion around the computer connector and pins.

 

[NVRL8]

I'm waiting to swap ecm's with a buddy. In the meantime I tested the voltage at the ecm pinout (C11) key on engine off. Voltage was 3.0 exactly and 5.0 with sensor disconnected. It should be 2.46. Voltage at the sensor plug was 5.0. Not sure if thats a big deal. I may try a new sensor and see what happens.

 

[mikestertwo]

I'm waiting to swap ecm's with a buddy. In the meantime I tested the voltage at the ecm pinout (C11) key on engine off. Voltage was 3.0 exactly and 5.0 with sensor disconnected. It should be 2.46. Voltage at the sensor plug was 5.0. Not sure if thats a big deal. I may try a new sensor and see what happens.

The voltage should be around 5.0V with the sensor disconnected. Make sure you check the grounds at the back of the head. If they are loose you will get erratic readings. Also check the resistance of the MAT sensor. If you disconnect the MAT sensor your scan tool should read around -40. At room temperature (70*F) the sensor should read around 3.4K

 

[NVRL8]

The grounds at the back of the head are secure. Those were a pia to get at! Scanmaster/Powerlogger gives similar readings as my first post with sensor disconnected, which is the puzzler for me. Sensor ohms good and is consistant with new sensor. The new sensor made no difference in readings. Thanks for your help, and I'll post up with my ecm swap results.

 

[NVRL8]

Problem solved! Bad ecm. I used my friend's ecm and temp readings were spot on. Thanks mikestertwo and sweet6.