Been chasing a misfire for months now with no answer in sight. It's occasional and random, can happen anytime, during warm up (open loop), after warm up (closed loop), at idle, cruising at speed ... whenever. Very quick. Blink and you miss it. Other than this the car runs as it should.

But now something new. This has happened three times in the last two days. Only when the car is stationary, at idle.
Suddenly it feels like it's about to stall out, revs visibly drop very low (100, 200), it recovers immediately and drives normally.
Don't know if the two things are related (this and the misfire) but I figured that was relevant.
Once yesterday, twice today over the course of a 20 minute drive.
Outside temps are pretty low around here right now (-10C / 16 degrees farenheit)

Does this sound familiar to anyone?

 

Please tells us any and all work you've done including parts replaced and where you got them.

 

Big year for this car.

Timing belt & water pump done in October (Aisin kit)


Timing Belt Job

Full tune-up done. Caps, Rotors (Bosch) Wires (NGK) Coils (NGK) Plugs (NGK)
Starter just done (AC Delco reman)
Coolant temp sensor (Hella)

Went through episode with ECU (unrepairable) back in summer, I know have two recapped and operational units.

Misfire was present before timing belt and starter jobs were done, can't say with certainty it wasn't there before the ECU situation ... It's not my car (gf's daily) and you can't count on her noticing things like that. She did notice when the ECU **** the bed and the car became undriveable .

Oh yeah ... before i figured out the ECU was the issue, I rebuilt the IACV (cleaned and new bearings) and it has worked flawlessly.

 

Why did you go with Bosch distributor rotors? That's the most aggressive crank pulley tool I've seen yet.

This sure sounds like a flaky ECU, I know you have what should be a verified good one but the symptoms match. What about bad grounds? I've seen a bad fuel pressure regular cause odd issues like this.

 

Why not? They work perfectly fine. That was actually the first "part" of the tune-up I did (6 months ago - i was in there chasing down noise behind the timing cover).

Yup. Looks scary but is the most gentle one you could ever use. Precise hole placement, very little clearance (slop) for the bolts that screw into the balancer, and it makes contact with the entire balancer face. Was the easiest part of the job lots of leverage. Zero effort to crack that bolt.[/QUOTE]
I know and hate that. Looking hard for it to be something else.
Been pondering that one. Is there one in particular that is known to be a bigger problem?
Had it happen on another car before, turned out to be the one right from the block to the battery. Zero visible corrosion of any kind.
Interesting. Could the fuel pump ECU cause something like this?

OH! ... also had some exhaust work done. Flanges after the downpipes were replaced.

Quite the year. This car has been ridiculously trouble-free up to this point. Owes her nothing.

Ever heard of one of the igniters failing on these cars?

 

Bosch parts in a Toyota is no good especially electrical components. Put a Bosch O2 or MAF sensor in a Toyota and 100% guarantee it will never run properly.

Maybe, I'm not an LS expert. Fuel pressure issues can be frustrating to track down you basically have to drive around with a pressure gauge connected.
Probably not, the same or similar part was used on many Toyota/Lexus of this era I've never seen one die. But, does the igniter rely on chassis ground to work properly? This is a known problem on older Camry's the igniter body has to be grounded or there is no spark.

 

I appreciate the sentiment but these are mechanical parts ... not sensors. Conductors of voltage, nothing more. Zero interaction with the ECU. But who knows

 

No the rotor is electrical is has conductors at specific lengths, positions and material composition. Rotors are just as important as spark plug wires and dizzy cap.

 

Hello,

Is there any logic to the Idle dropping, or it's complete random?
Was there ever a time the Idle would drop when the Throttle is released abruptly?

The fact that you can actually feel the RPM plummet means that this event lasts a considerable while, too long for it to be one specific Cylinder, likely excludes a number of components individual to each Cylinder, Spark Plugs, Injectors, etc. The fact that the issue mostly happens when the car just sits at Idle likely excludes the IAC Valve too, there is simply no reason for it to move on its own, and then return back to normal. It can't be a Vacuum Leak either, it's not how those manifest themselves.

Ground Wire seems probable, but that will likely be more noticeable during Driving as the wiring will have a much better chance of moving around and losing Contact, but it could be that the Inertia of the Engine prevents you from spotting it. Either way, to diagnose that, find all the Ground Terminals around the Engine, they should all be listed in the Manual, Start the Engine, and start pulling on each Ground point in every way to see if the Contact will get lost.

ECU is indeed a solid contender, as much as you would like to pretend that you didn't hear that.. The way to test it is pretty much the same as for the Ground Wires - unbolt it from the Mount and start pulling and prying at everything you can reach, hitting the Covers, maybe getting the Heat Gun to carefully warm it up, doing all of it while the Car is Started of course. Or you can just use one of the ECUs from your stash for a test..

Seeing that your car still has the Cold Start Injector, the MAF (or rather AFM in your case) Sensor you have is likely an older Karman Vortex style unit, which instead of producing regular *analog* signal produces a Meander Signal that corresponds to the Pulse of each Vortex on the Mirror. There is some probability that either the Mirror Surface is a little dirty, or, more likely, that the Mirror is not as flexible as it used to be, and below certain RPM Range is not as good at deflecting from the force of each Vortex. Simply put, when the car is sitting at Idle, there may be a point when AFM fails to register one or more Vortex, causing the entire Fuel System to stop working for a split second, until it gets back online.



With that, it's a long shot, and I have no idea how to definitively prove it seeing how occasional this issue is. Best way would be to find a guy with another 1UZ and trade your AFM for a few days, if your car will run well and his will show the same symptoms, you will know for sure that this is the issue, but finding a person like that is an even longer shot. Other way would be to test it on the bench by blowing Compressed Air into it while watching the Oscilloscope, waiting for the time when it would miss a pulse, but that's way outside of most shops' pay grade. I suppose you can also try unplugging the AFM and driving without it for a few days, but that may disable some other system, or conceal an issue with the ECU now that it's forced to be in the Limp Mode. Aside from flat out replacing it to see what happens, I can't really think of any other way, so I guess it would be up to how strongly you are attached to looking for ideas other than the ECU failure..

Another long shot may be the the O2 Sensors, if they are still OEM, it may be a good time to consider replacing them, not even because of the issue, but also because they are more of a consumable item and they do wear out with time, especially with the kind of mileage you have. My MAF died in a pretty interesting way about half a year ago, the Sensor Value would keep changing at every stop, so I ended up replacing it, and then got new A/F Sensors too a little while after, that made quite a difference on how the car felt, even though all the Parameters were within reasonable boundaries, and the only time I spotted any issues was when the car began stuttering at Cold Start.

[EDIT]: About Igniters - unless you do anything bonehead to them, like short the Output or get an extremely questionable Coil, I haven't heard of them dying, especially in such a manner.

The reason Bosch (or any other manufacturer that is considered OEM for other brands) is not that great for Toyota is because of the difference in approaches, they have their own ways of manufacturing and tailoring the components, not because of inherently bad quality, at least for the most part.. While those approaches may be just as good or even better, they are simply not compatible with other companies, hence the cause of the issues that arise when they are installed. For the Rotors though, all you need is to ensure that all the Dimensions line up, and that the material it's made of is conductive, seeing the condition of most Rotors on UZ Engines that still work flawlessly (most of which were never replaced in their lifetime), I am pretty sure the tolerance on those is plenty .. generous..

Those are pretty much the only ideas that come to mind so far, let me know if you have any questions or ideas to add to what's written above.

Hope this helps and best of luck!

 

An ignitor can fail. 1 of mine did, it actually cracked across the unit, right under the coil plug. Someone else also posted a similar issue not too long ago. This issue will shut down half of your cylinders and will buck like a bronco. It's not pleasent to drive... I would say oxygen sensors and maybe a bad ground, low idles are as random as my truck's failure to start. Just hard to diagnose when it's random.
I can feel the car die in gear below 40mph and if the tach is not staying at 1100rpm while downshifting and slowing down, I start holding the gas and brake at the same time to keep it from stalling. It's annoying, but after a few miles it will settle. Not sure if it's bad gas, fuel filter or grounding point.

 

You're talking about ignition coils cracking, which is a common issue. This is the igniter

 

woops my bad..