Rough Idle and misfires

[juanms3]

Hi everyone, I have been tuning two 08 Mazdaspeed3s for several months now, one of my friend's and mine. I moved my friend's to VersaTuner since January due to the limitations he had with Cobb and the remote tune with USA tuners has been complicated because the conditions in which the cars move here in our country and city (Colombia) are too different and variable in altitude and temperature in just a few kilometers of distance, BTW, the car has a built engine, forged pistons and rods, cylinder head porting, oversized valves and in general it is a full bolt on (stock manifolds) with a CST4, Corksport TMIC, Cobb Turbo back exhaust and supporting mods for that.

The car has always had problems at idle, when it is in CL and target the unchangeable 14.7 it starts to fail, with misfires and random codes of the same, I have tried everything, changing to new spark plugs (it has NGK LTR7IX-11 6510 gapped at 0.026) Cleaning injectors, new injectors, new coils but nothing works, something that worked was manually closing the VTCS, so when the car is below 60 degrees Celsius, it does not fail, only when it warms up. The only definitive way in which it was possible to maintain a stable idle and without misfires was going up to 900RPM and disable the CL in the ECU, and adjusting the mafcal in the idle zone so that the AFR is between 13.8 - 14.2.

My question is if maybe someone has had the same problem and if they have found the fault or the way to solve it.

As for my car, I bought it stock and tuned it from then until today, which has CPE TMIC, 3.5HTP Intake, Autotech HPFP, BOV and HKS Catback, running the K04 and stock dp at the moment (I have ready to install a BNRs4, Cobb DP and Treadstone FMIC)

I had been using the OEM spark plugs, but last week I decided to also put in some new NGK LTR7IX-11 6510 gapped at 0.026, but since then it started to present the same fault but not as accentuated. It misfires a bit and you can hear the popping through the exhaust. It has been throwing the code P0302. I already tried checking the gap, swapping the coils from Cyl 3 to 2, but the fault persists. I also raised the idle a little to 850 RPMs and it improved a little. It's not really uncomfortable and I can live with it, but it is very annoying that it is giving the code every time the car is used. I would not want to get to the point of deactivating the CL like in my friend's car.

Both cars have consistent tunes, with conservative boost levels around 16-19 psi, for the 91-oct gasoline we have here. I can post logs and tunes if anyone wants to check them out or can give me some guidance. Sorry for the long story and appreciate your help, guys.

[mituc]

Post logs.
Exhaust popping at idle during cold starts and even at warm idle is normal to a degree, if you will look at the live data you will see that timing has a variation when it happens and has to do with the timing adjustments the ECU makes to maintain the idle RPM, and it is indeed more accentuated with colder sparkplugs. 13.8AFR at idle however is not normal.
Deactivating CL doesn't sound even remotely like a good idea If you have a defect then you have to fix it rather than tuning around it, but hopefully it's a tuning issue. So post a log, let's discuss on real-life data.

[juanms3]

Ok, here an update. I've logged my car (Stock with bolt ons) from a bit cold (i've drived it today to my office like 4 hours ago) and another log in Idle with previous 30 mins of driving, also attach my tune and specs. I appreciate a lot your help

87k miles
Complete stock block
Stock K04
Stock DP and TP
HKS Catback
GFB BOV VTA
CPE TMIC
HTP 3.5'' Intake
Autotech HPFP

8.530Ft altitude
59-75F normal ambient temp (There are no seasons here)

Wetransfer link to download logs and tune:
https://we.tl/t-uq5bdqRIcd

[mituc]

Ok, so the logs you posted with idling look relatively fine.
However after looking at the tune I have to admit that this is by far the worst ever MAF calibration I have ever seen, ever.

Worst-MAF-CAL-ever-20251005.png (67.88 KiB) Viewed 694 times

By comparison this is how it should look like:

SomeRandom-MafCal-20251005.png (40.46 KiB) Viewed 694 times

You can clearly see the differences... Most likely when the ECU trips on one of those cels with lower airflow calibration than the previous lower voltage one it messes up the fueling big time. Also, these values have a very precise meaning, and the sensor response is dictated by a polynomial function. You can't just throw values in there Cel spacing values increase in a predictable manner, you can't have 2g/s jump between two consecutive cells and 0.3g/s after that. It will not work... I wonder how these idle logs look so good though... I reckon these ECU firmware and algorithms make wonders at interpolating wacky calibrations...

P.S.: you have a decent HTP 3.5" MAF calibration available here: https://www.versatune.net/forum/viewtop ... 238#p15238 . If you have big deviations/fuel trims with that one, and you actually have this intake, then start searching for leaks.

[juanms3]

Well, honestly the car runs very very well with that MafCal, lol. Within 5-7% STFT and 0-4% LTFT. I think I need a much much much better intake air straightner, I'll work in it. But another factor I have noticed that it influences a lot is the heat soak in traffic, It's horrendously slow here and these two factors made me do sh$t my MafCal. The car is running without any issue and leaks, I have previously tested it before the spark plugs change of the past week. I'll change the air straightner, put the ''default'' MafCal you shared for my 3.5'' and log the idle and normal drive/cruse zones and share here again so again I appreciate your time.