I've looked around at all the other threads about code 23 and I've gotten some good information trying to diagnose mine, but I'm not finding all the info I'm looking for.

1985 Z51, code 23 with a CEL that illuminates when the car is stopped after it warms up, which makes sense as the FSM describes this. I do get a 5V reference from the ECU at the connector for the IAT.

Checking the resistance of the IAT I get 2400 ohms with the engine cold, 84°F outside temp. After driving it a bit and even letting it idle until the cooling fans kick on at 225°, I get a reading of 730 ohms. According to the chart in the FSM that should put the intake air temp somewhere around 130-140°. I don't have a pyrometer so I have no way to verify if this is true.

(Interestingly when the cooling fan kicks on it actually drops to 720 ohms. Not sure why.)

I read in a really old forum post that if the IAT can't get below 500 ohms during operation then it's bad and should be replaced. I haven't seen this information repeated anywhere else so I'm not sure if it's true. Otherwise it seems like I'm on the hunt for a bad connection somewhere.

I did recently have the entire intake off but I've had it back together for a while and only several weeks after getting it back together did I get a code 23. Before that I had gone on several drives with no issue.

All that to say, does it seem like the IAT is dead or do I need to start looking for some sort of bad connection?

 

Have you looked at ecm data or ohmed back at the ecm pin c11 ?

 

I don't have an OBD1 scan tool so I can't look at ecm data. Is pin C11 the one that goes through the firewall? The book only mentions A11 and D13 which is the connector coming out of the loom under the distributor.

 

D11 is the ecm PIN number for mat on the 1226870

 

So are you talking about getting a resistance reading from the ECU connector itself?

 

yes if that seems fine your ecm might be faulty

 

This may be incorrect, but if I have 5 volts at the connector for the sensor, wouldn't that mean that all the connections between there and the ECU are good?

 

Pull the ecm plug and ohm, if it’s a reasonable reading your ecm is probably bad . Your really guessing without seeing any data.