2014~2018 Mazda 3 2.2 Skyactiv-D 150HP 2015 – grey smoke, constant regenerations, rough idle and warning lights

[StePago]

Hi everyone,
I’m looking for some help with an issue that’s been driving me crazy on my 2015 Mazda 3 2.2 Skyactiv-D 150HP (136,000 km). I’d like to describe the full situation in detail to see if anyone has gone through the same thing.

Main symptoms​

• When the engine is warm and idling (around 900 rpm), after about 10 seconds, a dense grey-white smoke starts coming out of the exhaust — literally a cloud that surrounds the car. It smells like unburnt diesel.
• During this, the engine rumbles or shakes slightly, as if combustion becomes uneven.
• This happens almost every time I stop, even after long highway trips.
• While driving, the engine pulls normally, but I can still see some grey-white smoke during acceleration.
• The DPF light NEVER turned on.

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Work already done​

• My mechanic performed a forced DPF regeneration, which lasted about one hour.
• After that, things got worse: now the smoke appears sooner, about 10 seconds after stopping, instead of after a few minutes.
• The DPF (FAP) and EGR are both still physically installed and active.
• I removed the EGR valve to see if it was causing the issue or if it was too dirty, but it turned out to be relatively clean
• The previous owner told me they turned off the EGR valve and the DPF from the ECU, but never touched, modified and removed the physical components, they've also removed the start&stop sistem (but sometimes it workes).

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Other symptoms​

• Sometimes the engine hesitates or jerks slightly under acceleration, especially when hot.
• Occasionally I get the i-stop and generic warning lights with the message:
  “Battery management system malfunction.”
  My mechanic says it might be unrelated, but I’m not convinced.
• At other times, the DSC, TPMS and SCBS lights come on together, and the car goes into reduced power (limp) mode.
  After turning the ignition off and back on, they disappear.
  I’ve noticed this happens:
  • on the highway when I lift off the throttle,
  • sometimes during an overtake,
  • or even once during a left turn.
• Since the forced DPF regen, the car seems to use more oil than before.

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Other useful info​

• No coolant loss.
• No strange noises from the turbo.
• No DPF light (as I said before, it never turned on)
• According to FORScan, the DPF completes regenerations, but it does so too frequently (basically at every stop).

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Questions to Mazda owners / mechanics​

Based on your experience:

• Is it possible for the DPF regeneration to start while idling, maybe due to a faulty sensor (DPF differential pressure, EGT, EGR, etc.)?
• Or does this mean the DPF never completes regeneration and keeps trying to restart it?
• Could the rough idle and “borbottii” (light rumbling) be related to the DPF process, or to something else like EGR or post-injection?
• Could the “Battery management / i-stop malfunction” warning actually be a side effect of the regeneration phase, or is it a completely separate issue?

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Any feedback or similar experiences would be greatly appreciated — especially if someone has had this exact mix of:

frequent regenerations + grey-white smoke + random warning lights (i-stop, DSC, SCBS) + rough idle at stop.

Thanks a lot in advance to anyone who can help me figure out where to start with a proper diagnosis, also because I don't know what else I can do.