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2019 RAV4 XLE Rough Idle and Misfire - CEL On

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Mike T. · rep 0 · May 22, 2:16 AM · 1 replies · solved · Question

Vehicle: 2019 Toyota RAV4 XLE

My 2019 Toyota RAV4 XLE, with about 60,000 miles, has developed a really rough idle recently. It feels like the engine is shaking more than usual when I'm stopped at a light. On top of that, the check engine light came on yesterday.

I used my OBD-II scanner and pulled a couple of codes: P0302 (Cylinder 2 Misfire Detected) and P0171 (System Too Lean Bank 1). The car also feels a bit sluggish under acceleration. I'm hoping it's not something major. Any ideas on what could be causing these issues together?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 2:16 AM

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ClearTheCode admin answer:

Experiencing a rough idle, misfire codes (P0302), and a lean condition (P0171) on your 2019 Toyota RAV4 XLE points to a common set of issues that affect engine performance. Here's a structured approach to diagnosing and resolving these problems:

  1. Address the Misfire (P0302):

    • Action: Since P0302 specifically indicates Cylinder 2, start by inspecting the ignition components for that cylinder. This includes the spark plug, ignition coil, and potentially the fuel injector.
    • Cause: A faulty spark plug (worn, fouled, or gapped incorrectly), a failing ignition coil, or a clogged/malfunctioning fuel injector in Cylinder 2 are primary causes for a misfire.

  2. Investigate the Lean Condition (P0171):

    • Action: A P0171 code means the engine's computer is detecting too much air or not enough fuel in the air-fuel mixture. This can be related to the misfire or an independent issue.
    • Causes:
      • Vacuum Leaks: Check all vacuum hoses, intake manifold gaskets, and PCV valve for cracks or disconnections. A common culprit is a cracked intake hose after the mass airflow sensor.
      • Mass Airflow (MAF) Sensor: A dirty or failing MAF sensor can send incorrect air readings to the ECU, leading to an improper fuel mixture.
      • Oxygen Sensors: A faulty upstream (pre-catalytic converter) oxygen sensor can give incorrect readings, causing the ECU to lean out the mixture.
      • Fuel Delivery: While less common for a single cylinder misfire, a weak fuel pump or clogged fuel filter could contribute to a lean condition across the bank.

  3. Interrelation of Codes:

    • Action: Sometimes, a severe misfire can indirectly trigger a lean code because unburnt oxygen passes through the exhaust, confusing the O2 sensor. However, a vacuum leak or MAF issue is more likely to cause both.
    • Recommendation: Start by addressing the most likely culprits for the misfire and then re-evaluate the P0171. Cleaning the MAF sensor is a good, inexpensive first step after checking for vacuum leaks.

When to See a Shop:

  • If DIY attempts fail: If replacing spark plugs/coils or cleaning the MAF doesn't resolve the issue, or if you can't locate a vacuum leak.
  • For advanced diagnostics: A professional shop has specialized tools to perform smoke tests for vacuum leaks, test fuel pressure, and accurately diagnose ignition coil or fuel injector performance, which can be crucial for pinpointing the exact cause of P0302 and P0171.
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