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2018 Mirage G4 rough idle and occasional stalling at stops

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Chris P. · rep 0 · May 22, 5:37 AM · 1 replies · solved · Question

Vehicle: 2018 Mitsubishi Mirage G4 ES

Hey everyone, I'm having an issue with my 2018 Mitsubishi Mirage G4 ES. For the past few weeks, it's developed a really rough idle, especially when I'm stopped at a light or in traffic. The whole car shakes a bit, and sometimes it feels like it's going to stall. It has actually stalled on me twice when coming to a complete stop.

There's no check engine light on yet, which is confusing. I've tried putting in premium gas just in case, but it didn't make a difference. The car has about 70,000 miles on it and I keep up with regular oil changes.

Could this be spark plugs, fuel filter, or something more serious? I'm trying to avoid a huge repair bill if it's something relatively simple to fix. Any ideas on what I should check first?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 5:37 AM

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A rough idle and occasional stalling in your 2018 Mitsubishi Mirage G4, even without a Check Engine Light (CEL), indicates a problem that needs attention. While the CEL might not be on, there could still be pending or historical diagnostic trouble codes (DTCs) stored in the Engine Control Unit (ECU).

Here are common causes and steps to diagnose:

  1. Ignition System:
    • Spark Plugs: Worn or fouled spark plugs are a very common cause of rough idle and misfires. Given your mileage (70k), it's a good time to inspect or replace them. The Mirage G4 typically uses iridium plugs with a longer service interval, but conditions can vary.
    • Ignition Coils: A failing ignition coil can cause intermittent misfires, leading to rough idle and stalling. If one coil is weak, it might not always trigger a CEL.
  2. Fuel System:
    • Fuel Filter: A clogged fuel filter restricts fuel flow, especially at idle when the engine demands less fuel, but can cause issues. While many modern cars have lifetime fuel filters, it's worth considering if you suspect poor fuel quality history.
    • Fuel Injectors: Dirty or clogged fuel injectors can lead to an uneven fuel-air mixture in cylinders, causing a rough idle. Fuel system cleaner might offer a temporary fix, but professional cleaning or replacement might be needed.
    • Fuel Pump: A weak fuel pump might struggle to maintain adequate fuel pressure, especially under load or during transitions, leading to stalling.
  3. Air Intake System:
    • Dirty Throttle Body: Carbon buildup on the throttle body can restrict airflow at idle, causing the engine to struggle. Cleaning the throttle body is a relatively simple DIY task.
    • Mass Air Flow (MAF) Sensor: A dirty or faulty MAF sensor can send incorrect air intake readings to the ECU, disrupting the fuel-air mixture. Cleaning it with MAF sensor cleaner can sometimes resolve this.
    • Vacuum Leaks: Leaks in vacuum lines or intake manifold gaskets can introduce unmetered air, causing a lean condition and rough idle.
  4. When to See a Shop: Even without a CEL, it's highly recommended to take your Mirage G4 to a trusted mechanic. They can:
    • Scan for pending or historical DTCs, which might reveal issues before the CEL illuminates.
    • Perform a live data scan to monitor fuel trims, MAF readings, and O2 sensor data.
    • Check fuel pressure, inspect spark plugs, and test ignition coils. Addressing these issues promptly can prevent more serious engine damage.
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