I have a '93 Z28 with a abnormal intake air temp.
At 75 F, ambient, the scanner shows 173F. Same reading using two different scanners. No code set. The OHM reading on the meter shows 3000 OHMs for the sensor. This is in range of what is shown in the GM service manual for 75 degrees.
All other scanned readings appear normal.
Any thoughts?

Thanks, Ted

 

Correction and additional information:

It was 70 degrees and a OHM reading of 3000.

392 degrees with the IAT unplugged key on engine off.

178 degrees F with the sensor plugged in, key on, engine off.

4.5 V at the IAT sensor plug, key on, engine off.

Ted

 

Was the 4.5 V reading with the connector off the sensor? Should be 5.0 V.

With the connector unplugged, you create infinite resistance in the circuit = very low temp (typical reading is -40* F). The sensor is a thermistor.... resistance varies inversely with temperature.

Sounds like a wiring problem, possibly a short.

 

Thank you for that!

I'll check for shorts in the AM.

Looks like it could be the Ground circuit.

 

Well I cleaned up the electrical connections using Detox, it made a little difference. V now reads 5.04 IAT 136 degrees @ 75 ambient. Ground wires need a little more attention...

 

The IAT sensor is subject to heat soak. On my 94, with the IAT in the stock position (rubber intake elbow) on a hot day (90-95*), sitting in heavy traffic, with AC on, the indicated temp, via the PCM could rise as high as 145*F. I relocated the sensor to the metal cap of the filter on my CAI, and the temperature matched the ambient air temp within 5*F.

Since the IAT is critical to your 93's speed-density A/F ratio control system, you have to come up with an accurate reading for the air actually entering the engine. It will be hotter than ambient due to the heat the air picks up on the way through the ducting. Metal ducting will generally allow more heat pickup than plastic/rubber.

Since you now have 5 volts at the connector, and the sensor is accurate - ohms vs temp - it's heat soak.

http://shbox.com/1/4th_gen_tech2.html#ect

 

Thanks for that info. I have been trying to keep the actual conditions (in the garage temp's) the same, by altering the time of day to match the original temp's to resolve this issue. I too have a rubber boot attached BTW the TB and the air intake duct but have not driving it to keep the conditions the same, watching and recording the temp's to track what changes made and the results thereof.

Thanks again, Ted

 

I'm confused. Are you saying that the resistance of 3000 ohms (normal for about 70F) is measured with everything in the same state (except that the connector is unplugged) as when the scanner shows 136? What does the scanner show when the engine is cold and not yet running? If it still shows around 136F, then I suspect either the wiring is defective or the scanner is in error. Was this taken with my Scan9495 app? If not, what models?

That reading of 178F (or 136F) would not likely set a trouble code.

 

No, the Scan9495 was not used.

Actron CP9110

Actron CP9145 were used along with a RS multimeter.
Ted

 

93 factory manual indicates DTC 14 does not set until CLT = 270*F.

To me, it was not clear from the original post that these readings were being taken with the engine at ambient temps.