# 1994 D21 hardbody pickup IAT sensor



## tim waldvogel (Sep 23, 2010)

hey i have a 1994 nissan d21 hardbody with a 2.4L engine. recently i took my car to be looked at by a friends dad\mechanic with his own shop and we took a look.

my check engine light is on and i need to get it smogged in the next few days

we checked the ECM which threw a code 41 at us for the IAT sensor (intake air temp. sensor) he took a temperature on my catalytic converter in\out cause my exhaust is popping and the light is still on;. he pulled my spark plugs which have a bunch of residue on them (they are only a few months old) based on the fact that the temp on my exhaust was hotter going in then it was coming and out of my catalytic converter... we assumed it wasnt passing exhaust and backing up into the engine causing misfires out the tailpipe. well we had my Cat checked out and it appeared to be fine, but i changed it anyways due to the strict smog standards in california.
its still popping with the brand new Cat and i have disconnected the battery and the CEL was still on when i started it. 

where do i go from here?


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## azrocketman (Oct 5, 2005)

So what did you do about the intake air temperature? Why all the attention to the exhaust and catalytic converter if an intake problem is indicated?

Steve


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## tim waldvogel (Sep 23, 2010)

Cause when he looked around my intake he saw no problems. I have since talked to 2 other people (1 Is a mechanic) and it doesn't seem to make sense that it us throwing that code for the symptoms it is showing. 

And it throwing the code for an iat I guess does not mean anything but somewhere within the electrical circuit that the IAT sensor is near. So their opinions were that my very old cap/rotor/wires might be causing the misfire which can set off the sensor to think the temperature is off in the intake. Which it would be if a cylinder was not firing correct?


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## azrocketman (Oct 5, 2005)

What I'm hearing is that nobody actually did diagnostics, other than a visual around the sensor. Did somebody actually look at the sensor element to see if it is clean with no debris? The engine computer is convinced that something is wrong with the IAT circuit but nobody else seems to care.

Is your "popping" sound a backfiring condition? If the IAT is a problem you will not have proper mixture control. Too rich would cause backfiring through the exhaust and too lean will cause backfiring out the intake.

Seems to me that somebody needs to disconnect the IAT and measure some resistances. I'm guessing that the sensor is a thermistor with a resistance that varies with temperature. You might even disconnect the sensor and see if it effects engine operation (force the computer into an alternate operating mode). The part appears to be about $55.00 from Rock Auto. 

I'm thinking the other folks are taking you down a rabbit hole.

Steve


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## smj999smj (Jan 1, 2006)

The wires for these IAT's were famous for breaking due to the constant back and forth bending of the wires. Remove the lower part of the air cleaner assy. and inspect the wires to it. There was also an update bracket created to remedy this issue in a TSB to address the issue.


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## tim waldvogel (Sep 23, 2010)

in my understanding from the other things i have read about my truck and my truck engine in a 90's nissan sentra book. the sensor it self should be fine, if it was a bad sensor it says i would be getting a different code saying there is a break in my circuit\open loop. if the sensor is actually sensing something within its circuit range THEN it will throw a code. it said to check intake air temperature.

well the mechanic (my friends dad) saw the code and immediately started looking around and obviously he would have checked that first. cause the code made no sense to him he said.
thats why he thought my CAT was backing up into my engine along with the residue on my spark plugs. also i noticed white on the tips of one of the plugs but not the others. which says to me that not all the cylinders are firing properly.
and given i bet my 211,000 mile original (almost positive) distributor cap\wires\rotor are due for a change anyhow.

thats MY logic. obviously i said i needed help\other opinions. and thats why i posted here. i know the people who gave me advice were not after my money cause they had nothing to gain from it. and since wires\cap\rotor for my truck are only about 40 bucks at autozone. and my truck has been having trouble starting (forgot to mention).... it usually take 2 or 3 times trying to turn it over. it literally feels like it winds up but isnt igniting the first couple times.

i just dont see the sensor playing into at the moment. and based on all the reading on the internet i did yesterday while trying to understand my vehicle better along with my ECM... it pretty much says the sensor is sensing a temperature change due to something else, or there is a problem somewhere in the circuit connected to that sensor. 
a broken sensor would cause an open loop of sorts and throw a different diagnostic code. 
and since i never started with just giving my truck a full on simple tune up... i figured that would be a good place to start. 

correct me if i am wrong please. i need many opinions


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## tim waldvogel (Sep 23, 2010)

smj999smj said:


> The wires for these IAT's were famous for breaking due to the constant back and forth bending of the wires. Remove the lower part of the air cleaner assy. and inspect the wires to it. There was also an update bracket created to remedy this issue in a TSB to address the issue.


thank you very much ill check that out now. what should i look for exactly cracked wires? broke wires?


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## tim waldvogel (Sep 23, 2010)

and if you guys have links that have literature to help me any further i would appreciate it.


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## SPEEDO (Jun 9, 2003)

smj999smj is correct, check the wires at the air temp sensor, common problem.
If your going to change cap/rotor, use oem... the a/f stuff is cheap, cracks and can cause arching, which causes you problems...


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## tim waldvogel (Sep 23, 2010)

your talking about the wires underneath the carb\air filter plate? i just inspected them and they appear to still be heat shrunk and just dusty. no cracks or anything i can see with my naked eye. 
i wiggled the plugs a little to see if any were loose or not snug. and i cant see any problem. where exactly is my IAT sensor located around the carb?


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## tim waldvogel (Sep 23, 2010)

Hey update !! 
Just took a look and found the wires coming from the thermal resistor/ my sensor and turns out coming from the plug is a broken/freedangling black wire (ground?) and I am assuming it is running rich and that would explain the black residue on my spark plugs/inside my tail pipr


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## tim waldvogel (Sep 23, 2010)

my IAT is the thermal resistor attached to the plastic air cleaner plate sitting under my air filter on the plastic plate correct?


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