4N15 (L200/Triton) warm-only rough idle — scanner shows 6 actuators stepping in lockstep, no DTCs. Commanded mode?
Hey guys, I've been battling with this issue for over a year. I have not done almost any modifications to the car. Only had switched original lights with chinese DRLs in the front (already put back the originals), changed the stereo to a Pioneer (install is good) and went to a Dyno/Tuner who says he has ONLY touched cells that are above 60% power (fuel pressure target).
VEHICLE
- Mitsubishi L200/Triton, 4N15 2.4 diesel, 2021, manual gearbox
- Base/DOC-only emissions spec: no DPF (ECU coded "Not Present"), no SCR/AdBlue, no NOx sensor, no EGR-gas-temp sensor
- Aggressive aftermarket remap (approx +55% hp / +70% torque)
- Note: CAN gateway module is absent (harness cut, timing unknown)
SYMPTOM
- Rough/hunting idle ONLY when fully warm (~85C). Cold idle is fine.
- Instantly smooths the moment ANY load / idle-up is added (hazards, brake, steering, A/C).
- ZERO stored/pending DTCs, no warning lights.
MEASURED (LAUNCH scanner, live data, warm idle ~800 rpm). It cycles between two states on its own, and I have BOTH target and actual on screen:
SMOOTH ROUGH
Rail pressure actual 35 MPa -> 119-123 MPa
Rail pressure TARGET 35 MPa -> 120 MPa (target moves WITH actual)
EGR position ~70% -> 0% (shut)
EGR target ~70% -> 0%
Intake throttle 18 deg -> 82 deg (choked) [1308mV -> 4180mV, linear/healthy]
Main inj timing -4 deg -> -6 deg (retarded)
Pilot qty (pre) 1.9 mm3 flat-> 2-3.4 mm3 HUNTING
Main qty (final) 10.5 flat -> 8.5-10.5 HUNTING
HP pump (SCV) target 1775 mA -> 1625-1675 mA
All six actuators step together and revert together. Rail target = actual in BOTH states (no control error, so it's commanded, not a runaway). The roughness is the pilot/main quantity hunting in the high state.
WHAT I READ INTO IT
Looks like the ECU is commanding a warm-idle heating/rich strategy: less air (EGR shut + throttle choked) + more fuel (rail up, post-inj) + timing retard = dump heat / go rich in the exhaust. On a DOC-only truck there's no
DPF/LNT/SCR that should need this at a warm idle, which is what makes it odd. Target=actual everywhere means the pump/SCV/rail sensor/injectors are all just obeying — not failing.
QUESTIONS FOR THE HIVE
Anyone recognize this exact 6-actuator warm-idle signature on a 4N15? Is it a known cat light-off / LNT-purge / de-NOx strategy, or a mis-gated enrichment?
Why would a base DOC-only cal command it at all — cross-market/wrong base file, or a real function?
Anyone map-diffed a 4N15 remap and seen the enable threshold / mode tables for this? Trying to confirm before a stock-flash test.
All the help is greatly appreciated. By the way this engine is kind of similar to Toyota's Hilux, also uses DENSO pump and and so on, so it should be similar setup.
