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

Ends in --- --- ---

Correcting your AFR

EFI Tuning Fundamentals

Forum Posts



Tech Articles

Discussion and questions related to the course EFI Tuning Fundamentals

= Resolved threads


im having problem in this place.

I have a Mitsubishi Evo X. (BC272 Cams, ID1000 injectors, AEM320 pump, Fuel Rail, Inline Fuel Filter, Injen Intake)

Im Using a COBB AP V3 to practice the courses. I had some problems today with the OTS Maps. I Used the Injector and Maf Scalling, Injector Latency, IPW Adder provided by COBB for my Injectors and My Intake.

#1. I have a Erratic Idle, and AFR too Rich on Idle, so i tried to set the Idle AFR Optimizing the VE, AFR gets leaner but keeps erratic. i need to know if there is another parameter to Optimize

#2. When Launching the car at very low RPMs, the AFR gets very lean, and i have to press the throttle more, or the car shuts down.

I have The Starter package, is there any class to help with this issue?

Hi Luis, I've personally had very little to do with the EVO X platform so i can't offer much help from my own experience. What I can say is that the Cobb OTS maps are incredibly well dialled in for the specific parts used in that particular staged upgrade so my assumption is that your own parts may differ from those used in the map you've applied. I've asked Mike from Cobb to pop in and see if he can offer you some more specific help on your car.

Hi Teacher, thanks for the assistance

yes its true about the OTS maps, but i have more parts instaled, and im just trying to adjust the car to those Modifications, Using the OTS Stage 3 or 4 initially.

So Lets wait the response of Mike from COBB


Sorry for my delayed response. The Evo X has an interesting airflow calculation strategy involving both MAF and SD (Speed Density) based airflow calculations. Both systems are active at all times and the ECU monitors for large deviation between the airflow calculated between the two. With that in mind, to get the car running well, you really need to dial each one in.

Personally I use the advanced toggles to disable speed density operation, tune the car MAF based. You'd use the principles taught in the HPA lessons i.e. tuning for minimal fuel trimming in closed loop and hitting air/fuel targets in open loop.

Then disable MAF based, enable SD based tuning, tune the car SD based.

At that point calculated airflow the MAF Calcs and MAP calcs monitor values should read about the same when you datalog both monitors. If so, you're ready to enable all systems. If not, see under what conditions they differ greatly and take a look at your MAF scaling and VE table in those areas to see if there's perhaps some smoothing that can help get the values closer together.

Alternatively, some folks disable MAF based tuning and tune SD only. I leave that up to you.

More on general tuning of the Evo X in the COBB tuning guide:


With the cams you have, idle speed and airflow will need increased for stable idle operation. I'd give 900 RPM a shot to make your life easier, then try 850 perhaps later.

It sounds like you entered the injector data which is good.

You mentioned launching from a low RPM, but is this a DCT or manual transmission vehicle? If manual, do you have a lightweight flywheel?

Let's start with that and I've not subscribed to this topic so I'll keep tabs.

Talk to you soon,


Hi Mike, Thank you for your tips

well ill try with SD and MAF combinations options that you gave me

About the RPM, i set it to 950-1000 RPM,

About the launch i refered to low rpm launch, when i release the clutch the AFR get too lean and i have to put more gas pedal or the car shuts down.

Ill keep you updated.

OK sounds good. In transient conditions like that, the Evo X leans more on the SD side of the tune, so take a good look at higher load cells closer to ambient pressure, under from lets say 800-2000 RPM. You'll probably need a bit more there.

My Other Question to Mike@COBB&Innovative is how can i datalog the AFR target, because i cannot see how to do it.

Im using Megalog HD and i need to see the graphs to compare Target Ratio vs AFR from My AEM UEGO connected via Serial-USB to my Accestuner Software

I think that Although Evos are no longer manufactured, COBB have to add some features or updates, it would be very easy for COBB to enable AFR target datalog like Subarus....because im feeling very limited compared to opensource.

Attached Files


I understand your personal workflow would benefit from a monitor. The Evo X's system is pretty simple in terms of air/fuel target. Feel free to reference the AF Target you set at a given RPM/Load in your calibration.

I will pass on your request. We'd love to add every feature requested for every platform. We'd love to have products for every car. The reality is like any company we have a certain size staff, which can get a certain amount of work done. Doing something always means not doing the other 1000+ things on the feature request list. Our list is literally over 1000 requests long and it gets trimmed down regularly to remove items we haven't received additional requests for. A ton goes into selecting the projects that do get worked on and we try to make the best choices we can. How many customers we can help by adding something is a huge factor in prioritization, as is whether something is needed to tune the car, or just nice to have. This particular thing may seem small, but consider we have over 1000 things on the list, many of which are small, and many of which are being requested by a large number of people. I hope you understand!

Hi Mike. I know but however i suggested this feature to COBB Support asistant.

Meanwhile im using excel to get the Target AFR.

But remember to not forget the Evo X, its a discontinued car but its still one of the favorites in the Market....

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?