u/Imunky21

Hey everyone,

I've been dealing with the following issue since January on my Mazda 3 (late 2019, Skyactiv-G 1.5, previous owner did ~25,000km/year mostly highway):

Symptoms:

• Started suddenly after a cold start, no gradual onset
• CEL permanently on, fault code indicates mixture/fuel trim issue
• Rough idle, occasional stuttering/bubbling at traffic lights
• Initially rpm was hunting between 1500-2500rpm by itself, that has since stopped
• Occasional brief surge/jerk at low speeds
• When I press the clutch the rpm briefly rises first, then drops down in steps, hanging at each step before finally settling at ~650rpm
• Motorway/highway driving is completely smooth and uneventful

What's been done so far:

• Mazda dealership added fuel injector cleaner additive four times – each time short-term improvement after ~100km of highway driving, but always reverts back

My question: Mazda is pointing at the fuel injectors, but another mechanic suggested it sounds more like an air intake issue – throttle body, MAF sensor or lambda/O2 sensor. The stepped rpm behaviour when pressing the clutch also sounds more like a throttle body issue to me than injectors.

Anyone with experience on the Skyactiv-G 1.5 with similar symptoms?