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2016 Mirage G4 Rough Idle, Misfires, and Poor MPG

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Tom H. · rep 0 · May 22, 5:31 AM · 1 replies · solved · Question

Vehicle: 2016 Mitsubishi Mirage G4 ES

Hello everyone,

I own a 2016 Mitsubishi Mirage G4 ES with the 1.2L 3-cylinder engine, and it's been giving me some headaches lately. For the past few weeks, the car has developed a really rough idle, especially when it's cold. It feels like it's shaking more than usual, and sometimes it even feels like it's going to stall.

The check engine light has come on intermittently, and I've pulled P0301 (Cylinder 1 Misfire) and sometimes P0300 (Random/Multiple Cylinder Misfire) codes. My fuel economy has also taken a noticeable hit, which is frustrating because the Mirage is supposed to be great on gas.

I've already tried replacing the spark plugs, but that didn't seem to help much. What else could be causing these misfires and rough idle in a 3-cylinder engine? Any common issues with the Mirage G4 that I should be aware of?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:31 AM

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ClearTheCode admin answer:

Experiencing rough idle, misfires (P0301, P0300), and poor fuel economy on your 2016 Mitsubishi Mirage G4 points to a combustion issue within the engine. Since you've already replaced the spark plugs, we can look at other common culprits for the 1.2L 3-cylinder engine.

Common Causes:

  1. Ignition Coils: A faulty ignition coil for Cylinder 1 (or any cylinder) will prevent proper spark, leading to misfires. Since you have P0301, this is a strong candidate.
  2. Fuel Injectors: A clogged or failing fuel injector for Cylinder 1 could be delivering too little or too much fuel, disrupting the air-fuel mixture. This can also cause a rough idle and reduced MPG.
  3. Vacuum Leaks: Unmetered air entering the engine due to a vacuum leak (e.g., cracked hose, faulty PCV valve, intake manifold gasket) can lean out the air-fuel mixture, causing misfires and rough idle.
  4. MAF Sensor (Mass Air Flow Sensor): A dirty or failing MAF sensor can send incorrect air intake readings to the PCM, leading to an improper air-fuel ratio.
  5. Oxygen Sensors: Faulty upstream or downstream O2 sensors can also cause the engine to run rich or lean, impacting fuel economy and causing misfires.
  6. EGR Valve: A stuck-open or faulty EGR valve can introduce too much exhaust gas into the intake, leading to a rough idle and misfires.

When to See a Shop: Given the persistent misfire codes and the impact on drivability and fuel economy, it's advisable to have a professional diagnosis. While some checks can be done at home, pinpointing the exact cause often requires specialized tools.

Recommended Steps:

  1. Swap Ignition Coils: Try swapping the ignition coil from Cylinder 1 to another cylinder (e.g., Cylinder 2). If the misfire code moves to Cylinder 2 (P0302), you've identified a bad coil.
  2. Fuel Pressure Test: A shop can test fuel pressure and potentially perform an injector balance test to check for faulty injectors.
  3. Smoke Test: A smoke test can effectively locate vacuum leaks that are hard to spot visually.
  4. Sensor Diagnostics: A professional scanner can monitor live data from the MAF and O2 sensors to check their readings.

Addressing these issues will restore your Mirage's smooth operation and fuel efficiency.

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