If you suspect your IAT.... read inside
09-18-2003, 07:17 PM
#1
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Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
If you suspect your IAT.... read inside
Hi everybody I just want to share some info about the IAT.
Must everyone know its a Thermistor and that its internal resistance goes down as the temp goes up.
I have read many posts where people have replaced it and their problem was fixed, but to me it still remains a hit and miss situation. I wanted a more solid approach. The chiltons book has a table of resistance/temperature to use as a base when taking readings off the IAT and the Coolant Temp sensor.. both are supposed to share the same temp/resistance linearity.
Let me first explain to you guys that my hobby is electronics and I am familiar as of how a Thermistor can fail and one way it can fail is by displaying a diferent resistance versus temperature than it was intended... So I used the 22 points in the Chiltons book to create a table of every single degree of temp versus resistance and I figured I could share this info with you guys so you can more or less figure out when your IAT went south....
My car for example: I took four readings and compare them against the Chiltons baseline for IAT resistance:
1) Temp 90* farenheit IAT resistance 2.112 Kilo Ohms
per chiltons it should read 2.0311 Kilo Ohms or 3.9% off
2) Temp 98* farenheit, IAT resistance 1.732 Kilo Oms
per chiltoms it should read 1.678 Kilo Ohms or 3.2% off
3) Temp 145* farenheit, IAT resistance 730 Ohms
per chiltons it should read 603.5 Ohms or 20% off
4) Temp 151* farenheit, IAT resistance 805 Ohms
per chiltons it should read 535.7 Ohms or 50% off
As you can see in my case the IAT reads perfectly fine at low temps.... but as soon as the car gets hotter the readings
go crazy all over the scale.
Now I have been having some slight pinging ad mid trottle only when the car is hot and the ac is on... I switched to the 160 thermo and it got much better... I seafoamed the hell out of my car and the problem was gone for a couple of weeks... Just yesterday it began knocking and pingin again when its hot...
My point being is that an IAT can be damaged and yet you can get good readings at some temps but not at others... this failure is actually common on Thermistors that operate at high temps due to heat stress on the Ceramic or whatever material they use to make em.
*** For each reading the Resistance was measured with the engine off (to avoid airflow in the elbow) IAT inserted in its location first.... Once I had a stable Ohms reading then I used an Infrared Temp sensor... I removed the IAT and Immediatelly took a reading inside the elbow through the IAT Elbow 0pening....
The temperature inside the elbow was very constant... with about half degree change per 10minutes... the engine acted as a big temp buffer so i know the redings were solid in each case.
I will Redo my readings again under similar temperatures and see what happens.... the Infrared Temp Meter gets a response in 1/2 second and it gives you live readings. This is important so you know you are getting a solid reading and Using a Digital Meter to get the Ohms resistance you know you are very acurate.
Just wanting to share with you guys and girls the info about the IAT. hope this will help you out to troubleshoot your beasts.
Marvin
Must everyone know its a Thermistor and that its internal resistance goes down as the temp goes up.
I have read many posts where people have replaced it and their problem was fixed, but to me it still remains a hit and miss situation. I wanted a more solid approach. The chiltons book has a table of resistance/temperature to use as a base when taking readings off the IAT and the Coolant Temp sensor.. both are supposed to share the same temp/resistance linearity.
Let me first explain to you guys that my hobby is electronics and I am familiar as of how a Thermistor can fail and one way it can fail is by displaying a diferent resistance versus temperature than it was intended... So I used the 22 points in the Chiltons book to create a table of every single degree of temp versus resistance and I figured I could share this info with you guys so you can more or less figure out when your IAT went south....
My car for example: I took four readings and compare them against the Chiltons baseline for IAT resistance:
1) Temp 90* farenheit IAT resistance 2.112 Kilo Ohms
per chiltons it should read 2.0311 Kilo Ohms or 3.9% off
2) Temp 98* farenheit, IAT resistance 1.732 Kilo Oms
per chiltoms it should read 1.678 Kilo Ohms or 3.2% off
3) Temp 145* farenheit, IAT resistance 730 Ohms
per chiltons it should read 603.5 Ohms or 20% off
4) Temp 151* farenheit, IAT resistance 805 Ohms
per chiltons it should read 535.7 Ohms or 50% off
As you can see in my case the IAT reads perfectly fine at low temps.... but as soon as the car gets hotter the readings
go crazy all over the scale.
Now I have been having some slight pinging ad mid trottle only when the car is hot and the ac is on... I switched to the 160 thermo and it got much better... I seafoamed the hell out of my car and the problem was gone for a couple of weeks... Just yesterday it began knocking and pingin again when its hot...
My point being is that an IAT can be damaged and yet you can get good readings at some temps but not at others... this failure is actually common on Thermistors that operate at high temps due to heat stress on the Ceramic or whatever material they use to make em.
*** For each reading the Resistance was measured with the engine off (to avoid airflow in the elbow) IAT inserted in its location first.... Once I had a stable Ohms reading then I used an Infrared Temp sensor... I removed the IAT and Immediatelly took a reading inside the elbow through the IAT Elbow 0pening....
The temperature inside the elbow was very constant... with about half degree change per 10minutes... the engine acted as a big temp buffer so i know the redings were solid in each case.
I will Redo my readings again under similar temperatures and see what happens.... the Infrared Temp Meter gets a response in 1/2 second and it gives you live readings. This is important so you know you are getting a solid reading and Using a Digital Meter to get the Ohms resistance you know you are very acurate.
Just wanting to share with you guys and girls the info about the IAT. hope this will help you out to troubleshoot your beasts.
Marvin
Last edited by MentalCaseOne; 09-18-2003 at 07:25 PM.
09-19-2003, 02:53 AM
#3
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Thread Starter
Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
Update:
I did some more testing today... I turned off the engine and let the elbow heat soak for about 5 to 10 minutes with the hood closed... till the elbows temp stabilized and here are my new results. Same IAT.
1) temp 131* farenheight, IAT resistance 978 Ohms
per Chiltons it should read 802.5 Ohms or 21.86% off
2) Temp 150* farenheight, IAT resistance 625 Ohms
per Chiltons it should read 546.4 Ohms or 14.38% off
3) Temp 167.5* farenheight, IAT resistance 480 Ohms
per Chiltons it should read 389.2 Ohms or 23.33% off
I am still getting the pingin at mid throttle with the A/C on
and a slight misfiring at Idle when the engine is warm. When the engine is cold there is NO pingin nor misfiring. It runs perfectly smooth. There is a very slight rich smell when engine cold. Its only noticeable if you squat down by the tail pipes. It did that brand new so there is no concern there... the smell goes away in a few minutes.
The car is parked and cooling off.. I will take more readings
as soon as the engine's temp gets closer to Ambient temp tomorrow morning. I will be checking for readings closer to the Chiltons baseline as it happened on the first testing. When the engine is hot It seems that the IAT readings are not only off by a big percentage but also erratic at high temperatures.
For the testing purposes I logically concluded that the IAT itself may have an acuracy error of roughly 5 percent... added on top of that I am including 3 pecent acuracy error inserted by the Infrared Temp Meter (its actually 2.5 %) plus adding a 1% operators reading error...(time I took to read the Ohms to time I took the temp reading) it was only about 2 seconds in between but I am giving it some allowance in case of any temp change in that time span. The digital Voltmeter's error allowance is so insignificant (0.01%) that I considerer it neglegible and I am not adding any more margin for error there.
In conclusion I believe we should not see more than 9% of total variance from the chiltons baseline readings Any more variance and I will consider that IAT a candidate for replancement.
At ambient temps my IAT reads a mere 3% diff off the Chiltons baseline so I know my IAT is defenetely showing failure only at higher temperatures, and it seems to be consistent. So I concluded its time to replace it even if its not the reason why my car is showing signs of slight misfiring and pinging at higher than ambient temperatures.
My next step is to purchase a brand new IAT replacement and then take new readings with it installed in the car. I will see if it fixes the misfiring and slight pinging.... I also kept track of my Miles per gallon with mixed Highway and city driving. 3/4 city
1/4 highway my average has been 13.185 MPG. my best MPG has been 14.99. I will see if it improves with the new IAT.
For you guys with scanners... you can only see what the sensor sends to the PCM. Not sure how easy it will be to detect a bad IAT that way.
Guys I am hoping to create an IAT troubleshooting page that you can just compare readings too and decide wheather its time to replace the IAT or if the IAT is the culprit of your problems.
Hope my info helps at least a few of you guys...
Marvin
I did some more testing today... I turned off the engine and let the elbow heat soak for about 5 to 10 minutes with the hood closed... till the elbows temp stabilized and here are my new results. Same IAT.
1) temp 131* farenheight, IAT resistance 978 Ohms
per Chiltons it should read 802.5 Ohms or 21.86% off
2) Temp 150* farenheight, IAT resistance 625 Ohms
per Chiltons it should read 546.4 Ohms or 14.38% off
3) Temp 167.5* farenheight, IAT resistance 480 Ohms
per Chiltons it should read 389.2 Ohms or 23.33% off
I am still getting the pingin at mid throttle with the A/C on
and a slight misfiring at Idle when the engine is warm. When the engine is cold there is NO pingin nor misfiring. It runs perfectly smooth. There is a very slight rich smell when engine cold. Its only noticeable if you squat down by the tail pipes. It did that brand new so there is no concern there... the smell goes away in a few minutes.
The car is parked and cooling off.. I will take more readings
as soon as the engine's temp gets closer to Ambient temp tomorrow morning. I will be checking for readings closer to the Chiltons baseline as it happened on the first testing. When the engine is hot It seems that the IAT readings are not only off by a big percentage but also erratic at high temperatures.
For the testing purposes I logically concluded that the IAT itself may have an acuracy error of roughly 5 percent... added on top of that I am including 3 pecent acuracy error inserted by the Infrared Temp Meter (its actually 2.5 %) plus adding a 1% operators reading error...(time I took to read the Ohms to time I took the temp reading) it was only about 2 seconds in between but I am giving it some allowance in case of any temp change in that time span. The digital Voltmeter's error allowance is so insignificant (0.01%) that I considerer it neglegible and I am not adding any more margin for error there.
In conclusion I believe we should not see more than 9% of total variance from the chiltons baseline readings Any more variance and I will consider that IAT a candidate for replancement.
At ambient temps my IAT reads a mere 3% diff off the Chiltons baseline so I know my IAT is defenetely showing failure only at higher temperatures, and it seems to be consistent. So I concluded its time to replace it even if its not the reason why my car is showing signs of slight misfiring and pinging at higher than ambient temperatures.
My next step is to purchase a brand new IAT replacement and then take new readings with it installed in the car. I will see if it fixes the misfiring and slight pinging.... I also kept track of my Miles per gallon with mixed Highway and city driving. 3/4 city
1/4 highway my average has been 13.185 MPG. my best MPG has been 14.99. I will see if it improves with the new IAT.
For you guys with scanners... you can only see what the sensor sends to the PCM. Not sure how easy it will be to detect a bad IAT that way.
Guys I am hoping to create an IAT troubleshooting page that you can just compare readings too and decide wheather its time to replace the IAT or if the IAT is the culprit of your problems.
Hope my info helps at least a few of you guys...
Marvin
Last edited by MentalCaseOne; 09-19-2003 at 03:52 AM.
09-19-2003, 08:11 AM
#4
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Thread Starter
Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
Update:
This is my IAT reading at a Ambient Temperature.....
1) temp 82.5* farenheight, IAT resistance 2437 Ohms
per Chiltons it should read 2438.9 Ohms or 0.08% off
Once Again the IAT reads fine at ambient temperatures..
to me its pretty obvious my IAT is defective.. It shows failure
only at high temperatures...
if any of you guys are interested in the Resistance vs Temp
table just send me an Email to MRivera982@yahoo.com
I will copy and paste from Notepad and reply to your Email
with a Text Message...
Marvin
This is my IAT reading at a Ambient Temperature.....
1) temp 82.5* farenheight, IAT resistance 2437 Ohms
per Chiltons it should read 2438.9 Ohms or 0.08% off
Once Again the IAT reads fine at ambient temperatures..
to me its pretty obvious my IAT is defective.. It shows failure
only at high temperatures...
if any of you guys are interested in the Resistance vs Temp
table just send me an Email to MRivera982@yahoo.com
I will copy and paste from Notepad and reply to your Email
with a Text Message...
Marvin
09-19-2003, 04:39 PM
#5
Registered User
Join Date: Mar 2002
Location: that place nobody knows
Posts: 335
Hey Marvin,
i know you're in Hawaii so i share your pain w/ the high ambient/underhood temps
i picked up a new IAT at Cutter Chevrolet for $27
which is surprising cuz they wanted $80 for 1 O2 sensor (so i went through Combination Motorsports in LV, i got 2 for $56)
anyway, even after that new IAT, i still had some pinging at 2,000+ and not when cold. turns out it was not detonation, but a slightly leaking header gasket!
replaced that with Fel-Pro 1406 and.... no more pinging!!!! zero
i'm so happy
autox this sunday!
i know you're in Hawaii so i share your pain w/ the high ambient/underhood temps
i picked up a new IAT at Cutter Chevrolet for $27
which is surprising cuz they wanted $80 for 1 O2 sensor (so i went through Combination Motorsports in LV, i got 2 for $56)
anyway, even after that new IAT, i still had some pinging at 2,000+ and not when cold. turns out it was not detonation, but a slightly leaking header gasket!
replaced that with Fel-Pro 1406 and.... no more pinging!!!! zero
i'm so happy
autox this sunday!
09-19-2003, 06:25 PM
#6
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Thread Starter
Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
i picked up a new IAT at Cutter Chevrolet for $27
Hey I been there too... I found one at Autozone online for $10 and another at Napa at $12.99 online. I went there in person and the lady told me they dont even have a part number for it
Went back online and printed the page cause it is
under Echlin Ignition Manifold Air Temp Sensor, one year
warranty. Autozone will deliver for 5.99 and has only 3 months warranty. Napa part number ECHTS4026 I am gunna go get it
in just a moment. I found another one somewhere online at $ 9 but they wanted $15 for UPS delivery. I laughed at them cause that part weights what?? less than an ounce??
Dude you are scaring me with the leaking header gasket thingy
I dont have the tools to remove my manifolds
how did you find out it was leaking? My exhaust manifolds look just well sealed from any angle.... also my pingin is under mid throttle acceleration with the A/C on. if I turn the AC off and press the gas pedal half way down there isnt any pingin at all.
I am hoping its only my IAT now. One thing is fer sure my IAT
went south. I am replacing it today and I will post what the results are.
Thanks for the info though. If I dont fix my problem at least I wont be staring at the engine with an IDIOTIC face
Did you go to Cutter by Nimitz??? Next time you go there ask them how come they told one your friends the 95 z28 Camaro
did not come with rear Shocks because it came with springs....
The Counter Parts Jockey got such and attitude when I told him
he Was DEAD WRONG that I swear he looked like he came from
New York City!!! (Looser).
I will keep you posted.
Marvin
Hey I been there too... I found one at Autozone online for $10 and another at Napa at $12.99 online. I went there in person and the lady told me they dont even have a part number for it
Went back online and printed the page cause it isunder Echlin Ignition Manifold Air Temp Sensor, one year
warranty. Autozone will deliver for 5.99 and has only 3 months warranty. Napa part number ECHTS4026 I am gunna go get it
in just a moment. I found another one somewhere online at $ 9 but they wanted $15 for UPS delivery. I laughed at them cause that part weights what?? less than an ounce??
Dude you are scaring me with the leaking header gasket thingy
I dont have the tools to remove my manifolds
how did you find out it was leaking? My exhaust manifolds look just well sealed from any angle.... also my pingin is under mid throttle acceleration with the A/C on. if I turn the AC off and press the gas pedal half way down there isnt any pingin at all. I am hoping its only my IAT now. One thing is fer sure my IAT
went south. I am replacing it today and I will post what the results are.
Thanks for the info though. If I dont fix my problem at least I wont be staring at the engine with an IDIOTIC face
Did you go to Cutter by Nimitz??? Next time you go there ask them how come they told one your friends the 95 z28 Camaro
did not come with rear Shocks because it came with springs....
The Counter Parts Jockey got such and attitude when I told him
he Was DEAD WRONG that I swear he looked like he came from
New York City!!!
(Looser).I will keep you posted.
Marvin
09-19-2003, 08:06 PM
#7
Registered User
Join Date: Sep 2002
Location: Tallahassee, FL
Posts: 870
Marvin.
You have way too much time on your hands. I was about to feel bad for you until I noticed that you're in Hawaii. J/K interesting information.. not something that you would normally consider.
You have way too much time on your hands. I was about to feel bad for you until I noticed that you're in Hawaii. J/K interesting information.. not something that you would normally consider.
09-20-2003, 01:06 AM
#8
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Thread Starter
Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
Update:
I picked up a brand new IAT from Napa. $14.47 Tax included.
Let me tell you guys... well worth it. My car no longer pings at mid throttle acceleration... or at least I can not hear it anymore.
Also it picked up some horsepower. It defenetely pulls at Mid throttle acceleration. Before it would take off from a full stop and once at mid throttle and about 40miles per hr it would hit a dead spot. Not anymore It defenetely pulls.
The car still has a very slight miss at Idle... not as noticeable as before. In a scale from 1 to 10 the amount of misfiring dropped from a 4 to a 1... much better than before. Only if you really pay attention you can feel it half miss-fire every now and then....
In conclussion I was driving with a malfunctioning IAT that if measured at ambient temp it would have passed the test with flying colors...
Please forgive my long posts.. this is the last one unless someone has a question on how I did it. Just to let you know guys this kind of problem would not have set a code in my OBD1 PCM...THIS PROBLEM IS MORE LIKELY TO GO UN-DETECTED unless you know exactly what to test for.
Marvin
I picked up a brand new IAT from Napa. $14.47 Tax included.
Let me tell you guys... well worth it. My car no longer pings at mid throttle acceleration... or at least I can not hear it anymore.
Also it picked up some horsepower. It defenetely pulls at Mid throttle acceleration. Before it would take off from a full stop and once at mid throttle and about 40miles per hr it would hit a dead spot. Not anymore It defenetely pulls.
The car still has a very slight miss at Idle... not as noticeable as before. In a scale from 1 to 10 the amount of misfiring dropped from a 4 to a 1... much better than before. Only if you really pay attention you can feel it half miss-fire every now and then....
In conclussion I was driving with a malfunctioning IAT that if measured at ambient temp it would have passed the test with flying colors...
Please forgive my long posts.. this is the last one unless someone has a question on how I did it. Just to let you know guys this kind of problem would not have set a code in my OBD1 PCM...THIS PROBLEM IS MORE LIKELY TO GO UN-DETECTED unless you know exactly what to test for.
Marvin
Last edited by MentalCaseOne; 09-20-2003 at 01:43 PM.
09-20-2003, 01:28 AM
#9
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Thread Starter
Join Date: Jul 2003
Location: Hawaii
Posts: 1,103
You have way too much time on your hands.
J/k dude. Just think about it... if my long post help someone to save the price of opty wires plugs and god knows what else..
then there will be someone who will be greatful and will remember....Mental Case One!!!
Marvin
09-22-2003, 02:12 PM
#15
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Join Date: Sep 1999
Location: NASHVILLE, TN
Posts: 393
I've always concluded the IAT did nothing on 94 and up cars. I figured it was just there in case the MAF failed and then it would use the IAT to help calculate the air flow in speed density mode. A test would be good... one test put a low value resistor in to trick it to thinking it was real cold and another run with a large resistor to make the computer think it is really hot.