Never had an issue before. Last Week, I drop my kid at school and come back to a still running car after perhaps 2 minutes, and my dashboard is lit up with flashing check engine and VSC codes. Engine is running rough with a clear misfire.

I was able to limp it 1 mile to the Toyota/Lexus specialist independent shop, where they pull a code for cylinder 3 misfire and a lean emission code. No big deal I think....probably a bad coil.

They have checked the coils and plugs, and that isn't the issue. Now they're guessing it's a bad ECU?

Anybody ever have a similar issue? I've never heard of an ECU failure where a vehicle still ran and only had a misfire.

This shop is run by 2 master Toyota/Lexus mechanics, and are extremely trustworthy....so I'm not inclined to not believe them. I'm just a bit lost. Misfires are either a result of no spark, no fuel, or no compression.

Vehicle is a 2005 RX330 with 168k. Never had an issue and has been maintained fully and garage kept.

 

I would check the compression and fuel injector before ruling the ECU...

 

Compression is good via leakdown test.

Computer is sending a signal to the #3 injector to stay open instead of pulsing, flooding the cylinder.

 

Sooo... what xactly tells computer WHEN to keep that injector open? Does it keep it open all the time, or only at the wrong time?
Car is always parked inside, right? I came across very strange engine issues simply based on wires chewed by rodents. My then Ridgeline had it. Rough running. $350 harness repair. PArked outside. I had LOTS of black pepper and traps around her after.

 

That was my thought as well...chewed wires/harness, but nope, shop says wiring is clean. Car is parked inside during the evening, but outside in a parking lot during the day.

Best guess is a resistor or capacitor finally went bad in the board. Will know shortly as the shop was able to find a used ECU for around $150. Tack on another $150 to flash/program the ECU.

Fingers crossed that the RX will be back up next week. I was not considering replacement anytime soon.

 

It was the ECU. Replaced with a used ECU for $150, and another $150 for reprogramming, and we're back up and running.

New ECU was supposedly $1500+

 

After 300 miles, I think I can confirm the ECU was the issue. The engine has never run smoother, and fuel economy is up (I wonder if cylinder 3 had been running rich for awhile? no codes previously though).

Added benefit is that the new ECU must have been updated to fix the wonky shift points that plague so many RX330's. So Smooth!

 

JMU2004, could you confirm whether or not that when running and limping you had the most horrendous juddering through the steering wheel? and what sounded like a mechanical smacking of parts against parts when you had this issue. My RX400h recently went from completely fine to undriveable overnight, with the same symptoms you were describing, plus the extra i've mentioned, i'm wondering if the valve isn't opening and that's what its slamming into? i really hope its not deeper into the engine, i love this car and i don't want to see it gone to the great metal graveyard. hopefully it could just be a coil pack replacement and perhaps a new ECU and we're back up and running. fingers crossed, but if you could elaborate on all of the symptoms you experienced when you had the issue i'd be very grateful.

 

For RT1289 - A Compression test or a Leakdown test would confirm if you had a Stuck Valve and it wasn't Closing and Hitting a Piston!