Stumble bumble

[ChiTDI]

Just experienced a stumble situation on an '02 Avalon, 132k mi.
Engine ran rough and nearly died as the op approached a stoplight.
Mile later the engine died as she tried to pull away from a light. Restarted and ran fine. I checked for codes - none, and I have put about a hundred uneventful miles since the "stumbling".
I'm wondering if the coolant sensor is failing and the the time(temp) when it moves from open to closed loop may be off.
Air Idle control valve is new (20k), all other sensors are original and maintenance has been right on schedule.
Car starts flawlessly, and runs really well except for this very,very infrequent stumbling. This happened 20k mi ago as well, and I haven't had any symptoms like this since I replaced the IAC valve.

[TedL]

First guess would be EGR system dumping EG in when it shouldn't. Valve stuck open, or control problem. Intermittent, of course.

[ChiTDI]

Update -
Got the engine to stumble this morning, just after the loop closed and the temp needle moved past the first peg. Was fortunate enough to feel the misfiring and feathered the gas enough to keep the engine running. Finally the CEL came on flashing (indicating misfire) and then stayed on when the stumbling stopped and the engine ran smoothly.
Codes were P0300 - multiple misfire and
P0304, P0306 - specific cylinder misfire
I cleared them and will try to check them again, but with this info I'm starting to lean (pardon the pun) towards a bad plug or bad coil. Clean the MAF maybe too.
Is my thinking sound?

[TedL]

Originally Posted by ChiTDI

Update -
Got the engine to stumble this morning, just after the loop closed and the temp needle moved past the first peg. Was fortunate enough to feel the misfiring and feathered the gas enough to keep the engine running. Finally the CEL came on flashing (indicating misfire) and then stayed on when the stumbling stopped and the engine ran smoothly.
Codes were P0300 - multiple misfire and
P0304, P0306 - specific cylinder misfire
I cleared them and will try to check them again, but with this info I'm starting to lean (pardon the pun) towards a bad plug or bad coil. Clean the MAF maybe too.
Is my thinking sound?

Since it's telling you that you have misfires on two different cylinders, it's not a (singular) spark plug. Since they are not paired on the same coil (assuming you have that setup), you'd be looking at two different coils failing at the same time. Plagiarizing Jason, I paste the following:
1-3-5
2-4-6

Wire positions:
() = paired cylinder

1(4)-3(6)-5(2)
2(5)-4(1)-6(3)

Those are the correct pairings for the wires.


But don't let me discourage you from whatever parts changing you want to do. I just suggest you buy from garys@toyotaofnewnan to save some money on all the parts you want to swap.

[ChiTDI]

Have no interest in changing parts for the sake of changing parts.
Have a reference now for future codes and a basis for determining malfunction. Not convinced that the codes are hard. This issue happened a couple of times to my wife and no codes were thrown or stored, so I'm still in diagnosis stage.

Ted- thanks for the wiring info and the reco for newnan. When it is time for the parts order, I sure will give them a shot.