My 2010 ES350 (6cyl, 3 ltr) is a low mileage, well-maintained car. I've had it for 5 years and it has 87,000 miles. In January driving on the highway at high speed (~80 mph) the car developed a pulsing stutter like the engine was running rough. Check engine light and traction control light came on. Pulled off highway at my destination and after the car sat for 1.5 hour started up and ran fine without warning lights or misfire/stutter.
It didn't happen again until next month (Feb) on the highway, again at high speed (around 80 mph), pulsing stutter of the engine, running rough, check engine light came on, so I pulled over. I turned the car off, sat 5 minutes. Restarted and the engine ran fine, no warning light. Repeated the next day while driving home from another city.

At home I ran an OBD2 diagnostic and got these codes: P0300 (random/multiple cylinder misfire), P0302, P0304, P0306 (cylinders 2, 4 and 6 misfires). Spark plugs were changed 13,000 miles ago at 70k miles (about 1.5 years ago) so I ruled out needing new spark plugs. I ended up changing ignition coils on the front bank of cylinders (2,4,6) and reset the OBD2 codes.

Two weeks later on another road trip had another misfire at high speed. OBD2 now showed P0300 and also P0301, P0302, P0304, P0305, and P0306 (all but cylinder 3). After reset, no problem rest of trip.

I do mostly city driving and have never had the problem when the engine was cold or at low speed, only on the highway at high speed and with a warm engine.

A week ago (May) I had a misfire when I was driving at 75 mph. Pulled over and turned off car, reset, and no problem. I'm hoping this is not an ECM problem, and OBD doesn't indicate that, but I'm frustrated not to be able to figure out what is happening. Anyone else have ideas?

 

Make sure all your vaccume lines on engine are attached

 

An owner had similar problems after a spark plug change job and subsequently found the mechanic had damaged the coils' wiring harness during the service. Fixing the harness cleared the issue.

 

Thanks. I'll check the vacuum lines

 

I guess it's worth looking at the wiring harness. It seem strange that the issue would only show up 1.5 years after the spark plugs were changed if the repair tech had damaged the harness. Also, it's an intermittent issue that only shows up at high speeds, which seems oddly specific. If it were the wiring harness I would expect it would show up at other speeds or driving conditions, especially since the majority of my driving is in town with lots of starts and stops. Thanks for the suggestion!

 

It’s hard to pin point the problem without live data monitoring of the engine to see what’s going on during the misfire.

For example, you could monitor the fuel trim to see how it’s reacting on both engine banks. You can monitor the voltage of each Air/Fuel sensor. You can monitor the MAF sensor readings. Etc.

I had a similar situation with my 1998 ES300 but it wasn’t at only high speeds. It felt more related to weather. If it was raining out or very humid, it would get worse. Engine would start misfiring randomly until I let off the gas pedal and coasted for a while or shut off the engine entirely and restarted. After about a year of driving like this, I finally found the issue to be rodent damage to the Bank 1 Sensor 1 Air/Fuel sensor wiring.

I realized it must have happened when I let my car sit outside with a unlatched hood while I waited for a new latch to arrive. This also explained all the symptoms I experienced. High humidity and water made the wires short out. They were chewed in such a way that they were touching each other. Letting go of the gas pedal spread them apart and broke the shorted connection. My fuel trim would also hit the max values whenever I was misfiring and it would only happen on that engine bank.

For you particular situation I would recommend to find a seasoned Toyota/Lexus mechanic who can do a thorough inspection and do some deductive reasoning to see which components may be impacting your drive ability issues.

I would also invest in a Bluetooth OBD2 reader such as BlueDriver. Very valuable for stuff like this.

Lastly, what type of spark plugs did you use? Did you install them yourself? And where did you source them from?

Same for the ignition coils. What type of ignition coils did you get and where?

 

Check your rear coils and especially their wiring. I bet one or its wiring (a known problem) was slightly damaged during installation and finally broke 70k miles later.

 

Hey man. Were you able to find out what the issue was?? I have the EXACT same issue with mine. Exact all the way to the same cylinders misfiring.

 

Having the same problem. Can someone chime in on this? Hate how no one on this forum ever report back with the solution. Why ask for help if you are not willing to atleast post a small update.

 

High speed, or high load, misfires are often and indication of fuel starvation. Since it is misfiring on multiple cylinders, I would suspect a bad fuel pump or the fuel pickup screen being clogged (as opposed to looking at the injectors).

Sometimes a bad ground can build up resistance and it only reaches a threshold of causing trouble when the electrical flow is maximized, as it might be under high speed conditions. Look in the wiring diagrams for grounding points on the engine and for the coils, and make sure they are all clean and tight.

Yes, and be sure to report back when you solve the mystery!

 

Read your Codes and post them here.

 

So some news.
The issue in the end was totally different. It was the handbrake in the end which was totally worn out. This gave intermittent issues.
Also the front brakes were worn out.

My previous garage didn't see those things at the last checkup. So another garage found it out.
It is running ok again.

 

I’m in the same boat 🥲 did you get yours fixed??

 

Yes Hand Brake

 

It was the hand brake that was giving you the misfires? Am I missing something here?