Changed the valve covers this weekend. Also did a small brake fluid evacuation and refill through the master cylinder. Took the car on a quick spin, and all was normal for 10 mins. All of a sudden, check engine light comes on, and car drives very rough. Has anyone had this experience? Took it by Autozone, and the recommendation is to replace coil. They all looked good when I had them out. Any other ideas? I don't want to throw parts at it.

 

Did you try swapping the coil with a neighboring cylinder?

 

No, they were unable to tell me which specific coil. I reached out to someone who was a Lexus tech, and the said it is coil number six. Strange it happens right after a valve cover gasket change. I'll need to check if everything is secure. Hopefully I didn't stretch a wire.

 

Wiring is a likely culprit but I would double check all connections.

 

-------
Code P0356 indicates that there is a problem with Ignition Coil #6 (P0351 is Ignition Coil 1, P0352 is Ignition Coil 2, P0353 is Ignition Coil 3...). If you have Techstream, you can trouble shoot the problem by yourself. Do the following:
1) Connect Techstream to the car and turn on the ignition (not to start the car, just turn the ignition to ON position). Record the the data (save data for future reference).
2) Within Techstream, go to "Powertrain \ Engine \ Trouble Codes" to clear Code P0356
3) After clearing P0356 code, start the engine. If the problem goes away. Drive you car as you normally do. If this P0356 code doesn't return after you have driven your car for 30-60 minutes (in Lexus shop lingo, run the car for 42 driving cycles), you may consider the problem solved. In other words, the problem was accidental. If P0356 code returns after you drive your car for 30-60 minutes, you have a problem either with the ignition coil or its power connection wires (loose connection, for example). To rule out a false wire connection problem, you'll need to read the voltage of the ignition coil's power supply connector. When you unplug the power of the ignition coil, you'll see that there are 4 wires within the power connector (on the engine harness). You'll need to use a multi-meter to read the voltage between Wire 1 and Wire 4 (ground) with the ignition is in ON position (again, just turn the ignition to ON position but don't start the car). The normal working voltage between Wires 1 and 4 should be 11V-14V. You should also measure the resistance between these wires. The normal resistance should be below 1 ohm. If you don't see the normal voltage 11V-14V and the electric resistance is above 1 ohm, you have a false connection or power supply issue. Check your wiring for the cause of the problem. However, if you observe the normal voltage and ohm range, the problem is most likely is within the ignition coil. Go to the next step to trouble shoot.
4). Turn off the ignition and swap Ignition Coil 6 with any other ignition coil, say Ignition Coil 4 (which is on the right of Ignition Coil 6). Clear the trouble code P0356 with Techstream. Start the car and see if the trouble code moved to the new ignition coil position. If you swapped the suspicious ignition coil from position 6 to position 4 (the next ignition position on the right of ignition coil 6), if the ignition coil is bad, you'll get a trouble code P0354. If this is the case, it confirms that the ignition coil is bad and you'll need to replace it.
Hope that this is helpful.
-------

 

Yes, extremely helpful. No Techstream for home, but I met someone recently who'd let me use his when our schedules align. How frequently is it a false reading, ie. example 1? Is that pretty common?

I'll swap the coils first thing in the morning to see if the misfire follows. If it doesn't, I'll try your recommendations.

Thanks-a-million!!

 

Update: Swapped coil six with coil two. I forgot I was gifted a bluetooth OBDII reader (FIXD). Cleared the codes and drove for ~40 mins. No codes came back, thankfully. I figured that the misfire would follow the coil, but something must have been loose. All wiring looked ok by the connectors.

 

----
Glad to hear that the code didn't come back after clearing it. It means that somewhere there was an accidental loose connection.
----