Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Trims at -25% and P0172 TOO RICH code

General Tuning Discussion

Forum Posts



Tech Articles

Discuss all things tuning in this section. News, products, problems and results. 

= Resolved threads


Hello all,

I recently fixed scaled my injectors, latency, cranking, and tip-in enrichment. So now, even though my cruise at 2000rpm is GREAT! The trims are +/-2% and the AFR is at a nice comfortable 14.7. So my issue now is NOT cruse.

My IDLE is all over the place...my trims are -25% and my AFR is sitting at 11.9

I tried adjusting my MAF scale incrementally by decreasing the cell at their respected idle voltage 3-5% through about 3 iterations but no luck. The AFR is still sitting at about 12.2 and the trims are still -25%

Funny thing is though; when I get out of idle and go for a drive the AFR normalizes at 14.7 with negligible trims of 2% while in light cruise


I just can't for the life of me get the idle tuning back to 14.7 with minimal trims.

What can I do to fix this?

(here's a pick of what I have my MAF curve down to around idle)

Attached Files

I wanted to give a quick update/edit on the above post.

I've been sitting in the car for the better part of two hours trying desperately to get the AFR back to 14.7

I have a total fuel trim of -25% on the Rom raider log an have been taking out incremental 5% from the idle MAF curve through the voltage ranges of 0.94v -1.37v (the idle portion)...

but when I log the AFR does not climb higher than 12.2AFR and the total trim is STILL -25%.

In total I have taken out more than 70% of the idle MAF curve(as you can see in the screenshot) Im getting close to zero, with nothing left to take out.

Something is wrong, and I've poured over the HPA videos on practical tuning and there are no answers to my problem.

Where do I go from here?

Attached Files

It sounds like you need to understand if it uses the MAF at idle. OEM ECUs can be strange undocumented beasts -- might be a separate idle fuel table, or yours is set to run speed density at idle or something.

Also, there might be a "minimum pulse width" which was correct for the oem injectors but not suitable for your current injectors. Are there pulse width or injector duty cycle values you can log and see what happens with your changes?

Very good question; and I appreciate you responding to my plight ^_^

To answer your question: I have logged the pulsewidth at idle: 0.570ms and the duty cycle hovers ~1.00%

To add a bit more context:

I originally had the MAF OEM stock; scale untouched and only adjusted the fuel injectors. Increase from 503cc/min OEM stock to my upgraded ID1050s @ 960cc/min. Went on to also decrease/adjust the base pulse width from the CL/OL transition table, cranking, and tip-in enrichment just like Andre explains in his practical reflash course under worked examples for MAF and injector scaling.

These changes made the idle great! 14.7 with trims @ ~+/-2% fantastic! So I proceeded to begin working on my light cruise/cruise 2000-3000rpm light loads. Now the trims were +7.00% so I decided to increase the fuel scale all the way to 1065cc/min and adjust the latency up, from 0.670ms to 0.925ms (to copy what IDs website has). I also adjusted the CL/OL transition, cranking, and tip-in again to compensate for the changes.

This is when the problems started happening and I couldn't get the idle under control; now my idles were -25% and my AFR was at 11.9-12.4. So I started taking out from the idle portion of the MAF scale. Every time, I would take out ~5%, reflash, log, and the trims would still be -25% with an AFR of about ~12.00. So I would repeat taking out the same 5% every iteration but the AFR wouldn't budge. Still at 12.00 So I kept taking 5% out, more and more, every time until I was like, "this is not how this supposed to work" I was running out of MAF scale to use and the AFR wasn't going anywhere.

Which brings me to what you alluded to in your previous post. It feels like there's a table somewhere that is compensating for the changes that I try to make in the MAF scale. It's like its fighting me; I know this because the engine sounds like shit, like its about to stall out every time I go lower and lower in the MAF scale in the idle voltage portion.

But you what to know what the real kicker is...

During light cruise, at around 3000rpm the engine runs perfect, LoL! AFR 14.7 with trims +/-2%...I swear, you can't make this stuff up!

David likely nailed it with the minimum IPW suggestion. Have you tried setting it to 0.3 ms?

David, the ECU is still on the OEM 32-bit drive. I only see injector latency and flow scaling that I can adjust. There is also A-D "per injector primary fuel offset" but I don't think that is what you mean.

BUT...there is a CL fueling target compensation; by load. Which would explain how no matter how low I go on the MAF the AFR doesn't change. The idle is around 800rpm.

Do you think it could be that?

Attached Files

I would ask the community that develops the definitions (i.e. the people who have disassembled the code in the ROM to figure out how it works, and what the tables do) if there is any "Minimum Injector Pulse Width" or similar parameter that could be added to the ROM definition. Perhaps someone knowledgable could describe how idle fueling works with the MAF and/or OL (Open Loop) / CL (Closed Loop).

I assume your Fuel Pressure Regulator is connected to the manifold pressure so the Differential Fuel Pressure remains constant at high vacuum areas like idle.

I don't know if that table is involved -- you could certainly try changing a value (make a big step) to see if it will affect result you are seeking.

Super helpful thank you David!

Yes, to address the FPR; I have connected it to the manifold; this is what the Aeromotive instructions described to do. I also, put in fuel pulse dampeners from Radium to help decrease the harmonics in the fuel system...don't know if that makes any difference.

Thanks again for the attention to my question.

It's definitely there, COBB has it defined.

Have you modified anything else with the engine? Are you running a vent to atmosphere blow off valve? I had a similar issue with my build (not an Subaru). My ecu uses the MAF for idle. The BOV spring I installed was too light and the vacuum assist would lift the valve and create a leak causing my idle trim and AFR to fluctuate and hunt.

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?