I've been looking around the forum and it makes my heart glad to see so many members tuning up and keeping there Fieros in good working order. However one thing that has been weighing on my heart that I think should be brought up for all 2.8 members is the Air Chrage Temp Sensor. See the 2.8 uses a system called speed density to measure the amount of air coming into the engine. It uses the MAP and the Air charge sensor together for this calculation. If you air charge isn't old worn out or malfunctioning your ECM cannot calculate the correct amount of air coming into the engine and this will lead to bucking, shuddering, loss of MPG, and loss of power. When I first got my 88GT it had 140 or 160 thousand miles on it, I can't remember exactly, and I drove it for another 60 thousand or so and the air charge temp sensor had NEVER been changed it was still the stock sensor from GM. When I did my tune-ups yeah they helped but man when I finally changed that baby it was like night and day difference.

For those of you that don't know this sensor is screwed into the air filter canister on the left hand side of the engine bay.

Good post. that sensor is an ope one, and rust can effect the sensor part.
it can even be simply checked with an ohm meter, and a thermometer. it uses the same values as the coolant and guage sending units:


this sensor can also cause that problem that people will be posting about the hunting idle that usually starts in the spring, tho not the only cause, I verified that if it is way off, it will cause that problem. (I swapped in a variable resistor and got the reading out of whack with the true ambient temp, and caused the hunting idle on my car, which does not have the problem normally)

WOW NICE TABLE!!!

This is also a case where a scanner or WinALDL can be very useful. They will tell you what temperature the ECM is actually reading from the sensor, which verifies not only the sensor but also the wiring between the it and the ECM.

Where is the air charge sensor and how to check it ?

Located horizontally on the Air Cleaner housing.

Unplug it and put a meter on the sensor's contacts. Look up on the chart for the air temp (at the sensor) and compare the resistance you are supposed to read with what you actually read.

Thank you , i learn another thing today . Is it when the engine is running though ?

[This message has been edited by Robert 2 (edited 03-28-2010).]

The sensor will give a resistance, engine running or not. You have to unplug it from the engine to get a reading.

Yeah, the Air Charge Temperature sensor ( aka Intake Air Temperature sensor) is just a resistor. It changes its resistance according to the air temperature. Hence the table above.

I remember having a problem with a hunting idle and occasional stalling on deceleration with my V6. When I finally got around to checking the intake air temp sensor, it was reading over 60°C (140°F) at room temperature! The engine was being starved for fuel during idle and deceleration.

Yes... good write up.
Also see cave. L4 DIS ignition. I cover MAT, same thing has ACT, sensor and error it causes for L4.

ACT temp reads about ambient air temp (local weather temp) all the time because where it is. (Idle air temp is warmer but not as much as L4)
MAT sensor reads intake manifold temp. At Idle, air temp is 150*F in intake when weather is 30-45*F.

And I think WinALDL will read MAT/IAT/ACT sensor.

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[This message has been edited by theogre (edited 03-28-2010).]

At 72 F i read 3000 seems OK .
Thank you guys for the lesson .

Just a note on that sensor: some people think they are useless and you can run without it even connected and some have, however I found that not to be true. We had burned a custom chip to accomodate our hi-flow intake, headers dif injectors and few other mods and found that the car would not idle correctly. Thinking we had too much we burned another chip and the idle still was NG? I put our wideband on the engine and noticed that the fuel mix at idle was all over the place -making the engine stumble one minute and rev high the next. I put an ohm meter to the MAT sensor and found the impedencing changing. One secound it told the ECU it was 100+ degs -it was actually in the 30s- then the next min it told the ECM that is was like -20! The ECU kept trying to reset the fuel mix taking idle all over the place. A new MAT sensor fix it. So, yes they do serve a purpose. BTW: they are cheep to.

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Nobody try running the car without its intake air temp sensor!

At the heart of the ECM's fueling algorithm lies the ideal gas law, which requires temperature to solve for the mass air flow.

Well, I got around the problem. A model 8007 Holley carb with a mechanical/vacuum advance distributor.

Works like a charm with 2 ignition wires and a thermostat. That's all.

Arn

Just Picked mine up this afternoon from Advanced Auto parts for $16.00

Autozone has it for $16.00 as well.

BTW Both Places call it a "Air Charge Sensor"

Mine definetly looked like it needed replacing. And it was seized up in the canister. Make sure you put a wrench on the welded nut on the canaster before you try wrenching the sensor off.

Car definetly seems to idle better.

[This message has been edited by deezil (edited 03-28-2010).]

Good post.

Just so everyone knows the "magic power chips" sold on Ebay are nothing but a single resistor that takes the place of the IAT sensor.
These "chips" do not work and will cause more problems. You can see by the above posts why the correct sensor is needed.

[This message has been edited by Oreif (edited 03-29-2010).]

good to know, thanks! BUT what if you are running an aftermarket intake and a K&N filter that bypasses the OEM canister alltogether. What do you do then?

The sensor was always put on the intake pipe of every Cai I have seen. If yours doesn't have it I would zip tie it somewhere close to the filter And call it done.

I've gone through almost everything on my '87 GT 2.8 5spd in the last 4yrs. I saw this thread and went out to Autozone and bought a new air flow/temperature sensor for $16. Figured it couldn't hurt, my old sensor was rusted, the car idled fine but hunted for awhile after stopping to find the idle. Anyways.........put in the new sensor. The car goes immediately to idle when stopping, mileage increased (22-25mpg to >26mpg), and the car feels a whole lot crisper all around. Still gonna do the 3800na swap next month, but this little sensor has made quite a difference! This thread deserves a bump back to the top. Thanks for the tip!!
Ray.

great info i am going to go check mine on my next day off.

My idle takes a while to settle down. I'm getting about 18mpg. I'm gonna change mine and see what happens. I know I've never changed it before and it does look a little rusty. I'll post my results.

Jonathan

Anybody got an idea how often this sensor should be changed?

I just replaced my O2 sensor, plugs, wires, pickup coil, and air filter. I decarbonized the engine, and had all the exhaust leaks fixed. My idle still hunts. But it could be due to the ECM not learning everything yet.

With a after market intake, couldn't you just drill and tap the tube and put the sensor in there? As close to the air filter as possible?

quote Originally posted by Formula Owner: Anybody got an idea how often this sensor should be changed?

Test it before you replace it. They may fail but don't seem to wear out. I went to the junkyard and got a few from other newer cars for comparison, and the resistance all matched up to what I got from the Fiero's.

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quote Originally posted by crazyd: Test it before you replace it. They may fail but don't seem to wear out. I went to the junkyard and got a few from other newer cars for comparison, and the resistance all matched up to what I got from the Fiero's.

I know it's not totally dead. I have an Auto X-Ray scanner, and I can see reasonable numbers coming from it, but I don't really have any to know if those numbers are accurate. My scanner showed a temp of 80 °F at 75 MPH this morning when I suspect the outside temps were around 60 °F.

Anybody have an AC-Delco part number for this part for an 88 V6?

car runs better , the idol is still alittle rough. took the hole stock air box out because the the sensor was frozen in. polished the air box, put a new piece of foam on the bottom for a better seal. put it back togeather and took it for a ride. seems a little more peppy. 16.00 dollars in autozone., thanks for the tip. i did the ground wire and it worked too.

I'm assuminig the meaning of "hunting" is the idle not returning to a fixed value but varying up and down for somoe period of time. Next chance I get I'll test mine but I wonder if it can cause the idle to stay high - which I'm still having trouble with.

Great info thanks!

quote Originally posted by Boostdreamer: My idle takes a while to settle down. I'm getting about 18mpg. I'm gonna change mine and see what happens. I know I've never changed it before and it does look a little rusty. I'll post my results. Jonathan

I just measured the ohms on my sensor and it is only showing 3 and dropping! Wow! That's a long way off from 3K. Guess I need one.

Jonathan

Great post!! Just an FYI. This is exactly the same for the 4.9 also. Same issues, same fix. The only difference is the 4.9's sensor is located in the intake manifold (next to the alternator) and follows coolant temp almost exactly. A scanner will tell you, without a multimeter, if it is reading off. I have to replace mine again also. I'm getting the hunting idle and not the greatest MPG bacause of this sensor. I just wish the ones for the 4.9 were as cheap.

EDIT: Correction. The 4.9 uses the exact same sensor as the fiero. Apparently the only difference is the cadillac "premium" added to the price.

[This message has been edited by Fieroseverywhere (edited 04-06-2010).]

quote Originally posted by DLCLK87GT: good to know, thanks! BUT what if you are running an aftermarket intake and a K&N filter that bypasses the OEM canister alltogether. What do you do then?

Our hi-flow intakes work fine with the stock sensor. If youre using a K&N typs cone filter directly on the TB, just drill and tap it for the sensor. BTW: Whiile those filters look neat; they are not really a good idea even with our intake. They let the engine draw hot air in instead of cooler outside -more dense- air. With our intakes we also recommend getting Rodney's mod for air filter system that opens up the inlet to the air filter. It does away with the water seperator. The stock intake can't outflow -CFM- the stock setup and thus it don't mater.

Could someone tell me how to use an ohm meter to check out my coolant temperature sender? My temp gauge is all over the place. Don

Bump for good info.

I tested my air charge sensor and it was reading 90degree's when it was only 60 degrees out... New one reads accurately. =)

[This message has been edited by cloaked (edited 06-27-2010).]

Bump for good info. I'll be getting a new one tomorrow. Small price to pay.....

yup. just about ALL cold running issues can be tracked back to this sensor & the coolant temp sensor

Anybody have a photo of where this sensor is located? Also how easy is it to change? Thanks in advance!!!

quote Originally posted by signtist2004: Anybody have a photo of where this sensor is located? Also how easy is it to change? Thanks in advance!!!

it is in the air filter can. easy to spot. follow the wire. only wire going to air filter can.