Help - even the dealer can't find the problem! (Toyota Fielder)

Hi everyone,

My 2016 Corolla Fielder (JDM) hybrid with the 1NZ-FE engine has started misfiring at idle and very light throttle conditions under load. It's done 131,000km from new.

Shortly before this started, I changed the engine oil and filter, and replaced the (original) spark plugs with new Toyota branded OEM denso plugs gapped to 1.1mm.

This problem can be reproduced by ensuring the car is at normal operating temperature and accelerating very lightly on a slight incline. It can also be heard by placing the vehicle in park and letting the revs drop to about 1000rpm. It is also very apparent when the car tries to turn off the ICE and switch to the electric motor at low road and engine speeds. There is frequently bucking and kicking and the typical “rattle of death” from the clutch coupling.

At no point has the CEL been triggered. Under all other conditions (including WOT) the car performs as it has always done in the 20,000km I’ve owned it.

Things I have tried already in this exact order:

1) Swapped back original plugs, no difference. Swapped new plugs in one at a time, no difference.

2) Bought a new coil and replaced one coil one at a time testing each time, no difference.

3) Unplugged EGR valve, test drive (CEL active) no difference.

4) Disconnected 12v battery to reset ECU, no difference.

5) Pulled EGR valve, pipe to manifold and cleaned spotless, they weren’t very dirty and the EGR valve still had freedom of movement. Visually inspected EGR cooler, very clean. Refitted everything, no difference.

6) Removed fuel injectors, inlet manifold and throttle body. Cleaned everything, confirmed EGR ports in inlet manifold not blocked, throttle body had some carbon build-up near butterfly, cleaned thoroughly. Cleaned injectors, bench bled with cleaning solution, replaced everything, no difference.

I dropped the car at the local dealer and they've spent 3 hours or so trying to find the issue. So far, they are seeing a fueling-related issue between several cylinders. The misfire seems to occur on different cylinders at different times.

Dealer has confirmed fuel pump is fine, fuel pressure is fine. Head gasket is fine.

The current plan is to change the o-rings on the bottom of the injectors as they seem to be able to trigger the misfire by spraying brake-clean at the bottom of the injectors.

I'm concerned that this isn't causing the issue, and the dealer is going to spend an awfully long time trying to chase this issue, and was hoping someone here might have read the above and has the answer. The mechanic I am dealing with is very competent but he's never seen this problem before.

Thanks!

 

No CEL at any point

 

Thanks, getting a 404 on that one

 

That article just really explains how the dealer can determine the condition the engine is in when it misfires, and the severity of the misfire. It doesn't speak to diagnosing what causes the misfire.

It does say that under very light load conditions it's possible to have a misfire that doesn't trigger warning lights, which seems to be what is occurring. Still no closer really to figuring out what is causing the problem in the first place.

 

Yeah I'm not sure the dealer is going to tell me that information. Was just hoping someone might have an out-of-the-box suggestion, or had direct experience with this kind of misfire. I guess I'll have to wait until the dealer figures it out.

Doesn't exactly fill me with confidence that representatives from the company that actually made the car can't even point to a cause after three hours on a computer.