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I've not been driving my 2003 Toyota Corolla since we were ordered to shelter. Today, I turned it over and found it rough idling. ECU faults show as follow:

fault log manager for 2003 Toyota Corolla showing misfire after storage

which reads:

  • Current Fault: P0303 - Powertrain (Cylinder 3 Misfire Detected)
  • Current Fault: P0440 - Powertrain (Evaporative Emission Control System)
  • Pending Fault: P0171 - Powertrain (System too Lean (Bank 1))
  • Pending Fault: P0302 - Powertrain (Cylinder 2 Misfire Detected)
  • P0171 - Powertrain (System too Lean (Bank 1))
  • P0303 - Powertrain (Cylinder 3 Misfire Detected)

Given that the mixture is lean, and that this vehicle has sat undriven for a few weeks, I'm inclined to think the issue lay in the gasoline itself or in the filter, rather than say an electrical issue.

The one complicating factor is that vehicle has had a tiny leak in the fuel system for some time, leading to a near constant indication of fault P0440. I wonder if, but rather doubt, the adhoc storage has exacerbated that issue.

What remediation steps should I take to isolate and repair this misfire?

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    I'm wondering the voracity of the P0171 ... if you have two cylinders with misfires, your exhaust is going to be rich, even if the misfires are sporadack. Did you clear the codes and run it again? Did you let it get completely warmed up? There's a high probability if you let it run for a bit, whatever is causing the misfire will clear up (like a stuck injector).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Apr 15, 2020 at 15:18
  • {{ if you have two cylinders with misfires, your exhaust is going to be rich,}} No. Not if he's got a P0171 at same time. Those misfires could easily be lean misfires, in which case the exhaust would show lean.
    – user9181
    Apr 15, 2020 at 16:44

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TL;DR: bad coil pack.

Diagnostics:

  1. Pop hood and remove engine cover
  2. Start car, note rough idling
  3. Starting from the left of the engine block:
    1. Remove the female ignition coil connector plug from coil pack
    2. If the idling noise changes, replace ignition coil connector
    3. If the idling noise DOES NOT change, that's the bad cylinder (*)
  4. Stop car
  5. Remove 5/8" bolt holding cylinder's coil pack; set aside
  6. Remove coil pack
  7. Remove spark plug
  8. Insert new spark plug into coil pack
  9. Set coil pack on engine block so you can see if plug sparks
  10. Start car
    1. If new plug sparks, coil is good and plug is bad
    2. If new plug DOES NOT spark, coil is bad and plug is indeterminate

In my case, the plug was pretty grungy (but not grimy like if a valve was leaking), so I replaced the coil pack and plug. Problem solved.

(*) In my Toyota 2003 Corolla, cylinder 3 is third from the left.

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