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M1 air temp model seems to be chasing its tail.

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I feel like im always battling the background air temp fuel trim. For example, if the intake air temps are around 125F at idle my closed loop fuel trim is plus or minus 1%. If I come to a stop after cruising and the air temps are 100F or so my closed loop fuel trim is now pulling 5-6%. I can see that as the air temp rises the closed loop fuel trim gets closer to zero. It seems to me that the air temp model is over compensating when the temps drop and the closed loop fuel control has to come in to correct the error.

Charge cooling gain is set correctly also. Any insight is appreciated


It looks like there are a couple of things you can do to dial this in. Look into the help and setup of "Inlet Air Temperature Sensor Trim" and "Inlet Air Temperature Correction". Since the correction also uses "Inlet Manifold Temperature", you may need to tune that as well, which to do accurately requires instrumenting the inlet manifold itself, and working with the corrections and time constants to get the values to be equal.

I would suggest logging the following channels to understand what is happening:

Inlet Air Temperature

Inlet Air Temperature Sensor

Inlet Air Temperature Sensor Trim

Inlet Air Temperature Correction

Inlet Air Temperature Correction Delta

Inlet Manifold Temperature

Inlet Manifold Temperature Stable

Inlet Manifold Temperature Stable Correction

Inlet Manifold Temperature Stable Correction Delta

Inlet Manifold Temperature Stable Initial Offset

Since you describe it as overcompensating on a quick drop, that sounds like a time constant that needs to be adjusted.

I used all the recommended time constants. Manifold temp is turned off, is there no way to calibrate this stuff without a thermo couple?

Attached Files

I suppose you could use an IR temp gun. You could also just enable the Inlet Manifold Temperature and change the channels to see if you can improve your issue.

I see you have the right channels -- why don't you try changing something and seeing what the results are? There will be one of three results -- better, worse or the same. Just figure out which it was, and make another change.

Just wanted to update this. I flipped on the manifold correction and with out any other changes it’s already better.

Thanks again

I have found similar problems with our 86 running the M1 package. I think it's important to understand that the inlet air temp is really being used by the ECU to infer the charge temperature and this is less straightforward than it might seem. Ultimately this is one of the aspects that comes from calculating mass airflow rather than directly measuring it - Every compensation needs to be perfect in order for the ECU to be able to do a perfect job. I try to have everything as accurate as I can get it, however I also accept that the closed loop control is going to pick up the pieces if there are some small errors remaining. Fortunately the closed loop control on the M1 is excellent.

Thanks for chiming in Andre. I do need to accept certain things are going to be limited. Check out the pics attached, this clearly shows that the port temp estimate must be too high because as you can see the closed loop fuel is trimming A/F richer as air temps climb, yet the injected fuel volume is the same as it is at zero A/F correction. I’m going to adjust some things in IAT engine system to see if I can settle the trim down.

Attached Files

I recently added twin electric fans and when they are on high they do move a lot of air. I think my sensor placement could be a big part of why the port temp estimate is too high. when the car is stopped the fan blows hot air right next to the air temp sensor. I think im going to end up moving the sensor to read inside the manifold itself instead of the charge pipe. I attached a pic of the sensors current location next to the fan.

Attached Files

In case anyone was interested moving the sensor inside the intake manifold made a huge difference. I can watch the air temps climb slowly with the car at idle and the fuel trims are now staying very consistent.


I placed my Bosch IAT in the intake a year or so ago per John's recommendation. I originally had it where old "AEM V1" would place it.... Heading to the dyno tomorrow to establish my new starting point on this same topic.

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