isaaccox

Hello fellow Lexus owners,


TL;DR

Currently my car is in a limp mode.

SYMPTOMS:
CEL on - but ECU doesn't communicate (confirmed by 2 mechanics), loss of power (and 50km/h is a top speed), rough engine sound, definitely running rich (I can smell it + fuel consumption is obviously high), only way to drive it somewhat normal is to put it first in L and then manually shift it into 2nd at higher rpms as I accelerate. If I put it in D first, it starts in too high of a gear and accelerates super slow. Also, there's no difference between 2 and D positions, which means there's a limited range of gears available to me compared to normal.

Additional symptoms:

• cold starts are noticeably harder, need to crank it for a couple secs
• black soot out of the exhaust on a startup

If I connect TE1 and E1 terminals in OBD1 port with a paperclip - CEL stays on, no blinking. But if I turn OD on the "O/D OFF" light will be blinking. That's all I was able to get using my diagnostics port.

My car was in good condition throughout all of my ownership but degraded quickly over a short period of time so here I am.

TL;DR ENDS



Below is a full story of my ownership (in chronological order), maybe something in it might point in the right direction:

Bought the car in mid 2022 from the first owner with a fat file of service records, certificate of delivery, etc. with 192K km on the odo.

Changed oil and PS and trans fluid, had to change driver's side inner tie rod and ABS sensor.

One of the bulbs in the right tail light would once in a while die and the corresponding light on the dash stays on until restart. That happened once in a dozen startups, only when I put the car in gear. Changed bulbs, my mechanic tried to solve this problem with tail light wiring, but this minor issue stayed.

There was another minor thing that I noticed quickly. After a drive in rainy weather, if I park it underground (so it's a hot start, humid conditions), it starts rough with low rpms and after a couple seconds (sometimes with a little help of throttle) it normalized itself. Of course, I started thinking about IAC valve back then, but that wasn't a big deal to me. And also happened only once in a while.

Then in 2023 I got a new battery, new struts, changed fluids, new stereo (tried to connect OEM disc changer and as a result, an OEM stereo was blown, so decided to go with a modern unit).

And after 6+ months of trouble-free ownership, something interesting happened.

I was on my way back from Oregon, enjoying another rainy day on the PNW. I was driving behind a jeep in heavy rain, so basically water was everywhere and I only could vaguely see a car in front of me. Drove like this for a couple minutes and at some point I felt the throttle jerking, so I had to turn off cruise control and apply more throttle, but it was unresponsive.

Safely steered and stopped on a shoulder, gave my Lexus some time, and the rest of the way home I was praying that I made it safely. This was the case because the rain stopped as I later figured out.

Then I was able to recreate this problem a month later. So it only happens in heavy rain, especially if I follow some semi or a truck/SUV with aerodynamics that increases water spray.

In mid 2023 I went on a 7000km road trip, everything was great. I think there was a problem with the throttle in heavy rain a couple times in Wyoming, but nothing major.

Got back from an American Southwest, changed a CV axle.

Then in late 2023 I went on a camping trip in BC, where my car was soaking in the rain for two days straight.

When it was time to go home, I started the car, drove 10km to a cafe, and right when I was parking I felt that rpms jumped for a second higher than usual. Had a quick breakfast, and when I started the car again, it had CEL on and rpms would bounce from high to low, then they would normalize and CEL would disappear. Somehow I got back home and only experienced a couple seconds of throttle jerking on the highway, but after that, my car was never the same.

Cold starts were always fine at that time. But hot starts always caused high rpms (even increasing rpms, like going to 2,3,4k rpms), so if you put it in D it will accelerate like crazy even in "idle" state without applying any throttle. Of course I had to control it with manual downshifts and breaks, but the engine was accelerating on its own.

So I decided to change an IAC valve. Waited for the part to arrive for a month, while the car was sitting in the rain day after day (Nov 2023). Had to change the battery too, cause the old one corroded (it's a new battery, which was weird) after sitting in heavy rain for a month.

Changed IAC to a brand new part - And that's when I got a new set of symptoms (a current set of symptoms): CEL, limp mode, transmission problems as described above. No problem with idle though!

My mechanic lost an original IAC, so there's no going back, unfortunately. We decided to test if it's the new IAC that's causing these issues, so I ordered a used one and tested it. Same issues with the third IAC on my car. Absolutely no difference.

Then I thought that the only thing that can explain such a wide variety of problems is the brain of my car - ECU/ECM/PCM.

Bought an ECU from FlagshipOne (I know it wasn't the smartest decision) - it did nothing for me. Sent it back.

Then I found a legendary thread about electrolytic capacitors. So I opened my ECU and that's where I found two leaking capacitors.

The next day I ordered a set of premium Jap capacitors (Rubycon, Chemicon - the recommended ones) and a professional that specializes in component-level repairs on PCBs changed them for me.

So today (March 2024) I plugged my ECU back in and absolutely nothing has changed. Same symptoms.



At this point, I'm out of ideas. A little desperate too as I love this car and don't want to junk it. It's in good condition, and every function of it (heated seats, all power functions) works.



Any ideas? What else can I try?

Is it a problem with the wiring? vacuum leak? knock sensor? speed sensor?

should I do another round of buying a new battery, IAC, ECU??

LeX2K

Get another ECU, hopefully one that hasn't had caps leak all over the board this can permanently damage it. Replace caps on the new ECU and see what happens. If you put in an aftermarket IACV it will be junk you'll need to go back to OEM. Have you ever had unexplained coolant loss? These engines are known to blow head gaskets.

CEL should rapid flash with the jumper in place not stay on solid.

Arsenii

Hello,

What tooling did the mechanic use to connect to the car? Just to be clear, it is not an OBD2 equipped car, and unless you have some very specific tooling, or a much advanced paperclip, there isn't much you will be able to pull from it unfortunately.

The seemingly random list of issues, combined with the Rain being a major contributing factor, makes be wonder if those issues are all related and linked to a Ground issue somewhere.

The reason is that any different ECU, even a defective one, will yield at least some difference, it is very much unlikely that two separate ECUs would suffer the same exact fault, besides, the rain won't affect the ECU without reaching something else first. The wiring could be the culprit, but it would usually trigger CEL before frying the ECU, and it wouldn't result in both the Engine and Transmission suffering the consequences, unless you have rodent damage in the wiring or something similar.

So far the only common link between all the issues are ECU and the Ground Points for that ECU, which could've aggravated common issues often associated with those ECUs, hence why there wasn't a noticeable improvement with any of the other ECUs you tried. To see if it is indeed the case, you have two options, both involve getting the Wiring Diagram for your car - first option would be to look up the location of all Ground Points in the car and start checking the Exterior Ones, the other option is to find all the Ground Wires on the ECU itself and connect a separate Ground to them straight from the battery to see if that will help.

If either of those methods won't yield any results, you will likely have to resort to some more advanced methods, like using Oscilloscope to monitor the ECU behavior, and loss of any of the signals. Either way, with the symptoms as pronounced as what you have, the issue can't be that far out, all that will depend on how deep you are willing to dig.

P.S. With all that said, I have to agree with LeX2K on the ECU issue, it is a pretty low hanging fruit, and sooner or later you will have to get a replacement and repair its capacitors anyway. Depending on how long you are going to keep the car, some people have a spare rebuilt unit sitting in the storage ready to go when the old one will inadvertently kick the proverbial bucket, such is the nature of first-timers..

Hope this helps and best of luck!

isaaccox

Thanks, guys

Now I have new leads thanks to you.

@LeX2K

No coolant loss. I've been keeping an eye on it for a while now.

IACV - I think (I hope) I'm back to an OEM used IACV. At least that's what I bought as my 3rd IACV. As I mentioned, after installing a brand new IACV (Aisan "22270-62020") I got a current set of problems with my car, so I figured the same - I need to go back to an OEM part.
But like I said, 3rd IACV made no difference. I wish I could go back to my original IACV, though.

+ with all the problems that my car has it does have an excellent Idle. A bit too rich, but still the Idle is smooth.

++ I cannot imagine an IACV causing transmission problems no matter how bad it is.

ECU - I was going through my photos and found that an ECU from FS1 had a "175000-4592" secondary index while my computer had "175000-4591" on it. It's not the main part number, so I kinda ignored it seeing that the actual part number 89661-33180 was what I needed for my VIN, so I went with it.

Do you know by any chance what this secondary number means? Would it mean that they're not compatible?
Need to know that before I order a new ECU again, because what I see on eBay right now only has -4592 number.






@Arsenii

I'm 99% sure both mechanics didn't have the necessary tooling to scan my OBD1 car, so maybe there's still something to be further explored. They were using the same paperclip method and trying some obd1 to obd2 adapters which didn't work.

Sorry, I wasn't clear about what happened after installing a different ECU. I said that it made no difference meaning it didn't fix anything. My mechanic plugged in an ECU without me present. He told me that it simply flooded his shop with smoke. He didn't say what color was the smoke or was it any different than normal running rich condition that I have now with an original ECU.

So far I'm leaning towards trying a new ECU and checking the ground wires.
By the way, does an ECU for my car need to be programmed to my VIN? I have no idea if my OBD1 car with a 3VZFE has an immobilizer system. I'm still using an orginal one-button key that, no aftermarket security stuff.

LeX2K

89661-33180 is the Toyota part number the 2nd one is a Denso number not particularly useful. Someone printed the label for the 2nd ECU pictured I'm guessing because the original peeled off. Take the cover off and have a look, better yet post some pictures.

These cars are straightforward electronically not much goes wrong with them. OBD-I is quite primitive but good enough for this engine you're likely only ever get 2 codes, knock sensor and O2 sensors.

Check the ground back of the intake.

Arsenii

The secondary number is basically the Part Number as well, but the one assigned by Denso, the company that manufactured the ECU, could be useful when looking to retrofit a part that has completely different Toyota Part Number, but may have a very similar Denso Part Number. That said, in your case it looks more like a revision number, aka higher is better, they may have modified the ECU slightly and reflected it in the number, even if both will work just fine in your case.

While there are ways to pull more information out of OBD1 port, here is a thread, it's usually a point of diminishing results, as it does have quite limited functionality compared to OBD2 standard that surpassed it. In your case, the issue is evident enough, and in more than one place, so a paperclip should more than suffice to see if the ECU responds at all, and what codes it will start shooting out.

Sounds about right, though I would suggest flipping the order, and trying it out on the old ECU, as there is a very small chance that a Ground fault may be a contributing factor to the ECU's demise, that is if it is indeed bad, as both ECUs you have exhibit the same behavior. A simple enough precaution that may save your new ECU.

Hope this helps and best of luck!

isaaccox

Hey guys,

Just got a multimeter today, so I have a minor update for you.
In the photo below - the readings from the red points show the same 12,35V that's on my battery, but the blue one (MAF) showed 5,35V.



So I decided to dig deeper and unhooked MAF to check the harness - only one contact (2nd from left) showed 11,5V , others had the same 12,35V.



But then I did something stupid...



So while I'm out of working MAF,

Is there any way to override it and start the car without an air filter and MAF? It definitely doesn't want to start now.

If we ignore my mistake, am I working in the right direction? Is it normal for MAF to display different Voltage readings?

@LeX2K

I sent that other ECU back before I started this thread. Because It didn't fix anything. I decided I wanted my money back. Opening it would void any chance to get my money back.

The multimeter reading was 12,35 on the intake, so I started manually checking all grounding wires.
I checked an EC ground, E2 and E3 too. Couldn't find/reach ED, It's kinda underneath the intake. EE1 was just a harness coming from the firewall, not grounded to the body in the engine compartment, but since all contacts of MAF harness showed good numbers, I don't think it's a problem.



Basically, I was hoping for a solution similar to the one below (from an old CL thread), but now I think maybe it was a MAF all this time.

LeX2K

That's a common mistake sometimes it can be repaired or you'll be needing a replacement airflow meter. You can jump the fuel pump in the diagnostic port but without the airflow and intake temperature sensor (it is contained in the MAF) the engine won't run properly or at all.

This pdf has all the test procedures possible
https://drive.google.com/file/d/1ntw...ew?usp=sharing

If the MAF is failing you will get a CEL right away. There is a ground coming off the main engine harness that bolts to the intake did you find that one?

BTW I opened up a 1993 ES300 ECU I have on hand the capacitors looked perfect no signs of leaking. A sample of one but I was curious.

booboofoo

Chiming in to offer my personal ECU history with my 92 ES300.

I've owned my particular specimen since new, and as you hopefully might see in my attached photo, my car hasn't had a hard life.




However, what I can tell you is the ECU on my 3VZ-FE did cause problems when the capacitors inside the ECU started to leak electrolyte.

Perhaps that's due to the sub tropical climate where I live in Australia?

The range of problems were mostly misfire related issues.

In my case, I bought a 1995 Toyota Camry Automatic transmission 3VZ-FE ECU and it has worked faultlessly in my 92 ES300 ever since I put it in at the end of 2022.

I also bought the replacement capacitor kit for my original ECU but I have yet to solder them in.

Now, all that being said, I did have another issue at the same time when all my misfire problems were happening.

Naturally I assumed it was all related to the ECU but it turns out I had a problem with a Chinesium distributor which I purchased purely for aesthetic reasons. (The original was looking a bit old).

The Chinesium distributor lasted just 3 years before it started sending faulty crank trigger signals to the ECU.

So what happened is I put the replacement ECU in, a lot of the misfire issues were solved but then the engine would mysteriously die and not restart.

Which was disastrous in traffic obviously. Naturally I assumed the replacement ECU was also faulty.

I did loads of research on the ignition circuit system, and it turns out the distributor plays a major role in a 3VZ-FE because it provides three different trigger signals.

When I tested the Chinesium distributor with a volt-meter it was clear it was a malfunctioning component, so I put the original OEM distributor back in and all my problems have since gone away.

I sincerely wish you every bit of luck regarding your engine issues.

Based on your opening post, what I would test for is what happens if you completely bypass the IACV valve with a bung, and then mechanically set the idle (at the throttle body) to be high enough that the car will start cold. Obviously it will run quite high when the car is warm, perhaps 1500rpm, but you "should" be able to do some tests.

My thinking is, if the engine is still racing up to 4k rpm even with the IACV bypassed, it must be getting air from somewhere to do that.

Perhaps the cruise control circuitry is playing with the throttle body? Perhaps the throttle body is failing at a mechanical level?





In closing, in May of 2023 I purchased a TOYOCOM ODB1 live data transmitter which sends live data from the ECU to a bluetooth Android notebook.

A very useful tool, and they're currently available for sale.

You can monitor every single bit of data the ECU is crunching - in real time. Including CEL codes.

Arsenii

I am a little confused on the readouts you provided, which Pin on the Pinout below had which voltage? The thing is that most of the sensors work off of separate 5V line coming straight from the ECU, not 12V, so the initial MAF readouts are correct, you should have 5V on Pin 4, while Pin 5 is your Ground, Pin 6 is the Sensor Output, Pins 1 and 2 are connected to a Switch that powers your Fuel Pump, strange system that ensures the engine is indeed spinning before engaging the pump, hence why the car doesn't even attempt starting.



The bad part is that MAF is not the only sensor that is supposed to be getting 5V, Throttle Position Sensor (TPS) is one of them as well, more than that, it is powered off the same wire as the MAF sensor, even though it seems like you have 12V on it instead.

The pin marked on the picture, Pin 6 (your connector is upside down from what is on the pinout), is the Signal Output from the MAF sensor, it is strange that you have anything at all on it when the MAF is disconnected, let alone 12V when you have 5V coming into the sensor.



All those issues lead me to believe that you are not out of the woods with the Ground issue just yet, even if it is bolted in place, the wire connecting to the terminal may be damaged, causing random voltages that are higher than they need to be, this is the case when a Multimeter can really start messing with you, as it doesn't put any Load on the circuit, picking up phantom voltages, I've had that happen before, hence why I always prefer to go with a Test Light where possible. Just make sure to be careful with a light around 5V lines, as they may be a little sensitive, make sure to get a lower power one.

Those MAF sensors, or rather AFM sensors, as they are not measuring the volume of air, per say, it's just a deflection plate that opens as more air comes in, they are a lot simpler than newer types, and are usually not as hard to repair, even if you will have to cut the top cover off, it uses something similar to RTV sealant to secure it in place. Now that there isn't much to lose, it won't hurt to take the lid off and see the extent of the damage, it may still be salvageable.

5V line, as most of the sensors, don't have a separate Ground location on the frame or the engine, it is going straight back to the ECU, which in turn is Grounded on the ED Point under the Intake Manifold, it's one of the most crucial Ground points in those cars, my 2000 ES300 would behave erratically without it, causing all sorts of issues with transmission along other things, and there are reports of your 2nd-gen not even being able to start without it, so it is very important to check that it is securely bolted in, and that the wire coming out is not damaged in any way, as they do tend to get cooked being so close to the engine.

P.S. Lucky you, I somehow managed to miss it, didn't know they would make another batch.. Oh well, cheers for the other batch to show up at some point.

Hope this helps and best of luck!

booboofoo

Why thank you. I only found out about the batch by being signed up to Jean's Facebook Page.

I have since stopped using Facebook so I'm no longer in the loop regarding TOYOCOM.

The single biggest benefit I found was being able to record a trip in real time on my Android notebook and then analyse the data in the comfort of my home office.

I was able to verify every single aspect of the engine bay is working correctly - including all the fussy 5V signals you mentioned.

It's a wonderful feeling knowing my 3VZ-FE runs 100% optimal, but geezus it runs rich however.

Analysing the data suggests the ECU works in binary mode regarding fuel richness.

As you know, the O2 sensors are REAL early binary sensors... they're either rich or lean from the ECU's perspective.

If the ECU senses a lean condition it stretches the injector duty cycles until a rich signal occurs again - but it doesn't care how rich it is.

On top of that, if your throttle body is over 15% open, the ECU implements "Acceleration Enhancement" mode, which is equivalent to running more rich than normal.

And that can't be turned off... it's deep DEEP into the fuel map software.

LeX2K

It is very easy to lean out the 3VZ, you get more power and better mileage.

Back to this
I don't know why that is happening but it is obviously not normal. That's why I don't see much if any value in a rare OBD-1 reader or replacing ignition parts that is not going to fix the above at least I don't see how.

booboofoo

Presumably you're referring to the AFM ratchet wheel hack?

I've tried it and I've taken the car to a Wide Band Sensor tuning shop with a dyno.

What actually happens is the ECU overrides the AFM door voltage setting if the O2 sensors are saying lean.

In real time the ECU constantly cycles the injectors between lean and rich.

Most importantly, the "Acceleration Enhancement" feature cannot be turned off.

Happy to upload a TOYOCOM video to demonstrate.

LeX2K

I ran this hack for many years it works. Engine ran quieter had more power my fuel economy improved. It is a well documented successful mod.
If you want make a thread about it although not sure how many 3VZ owners are left out there. I do miss mine.

booboofoo

In fairness, there's no need for me to NOT trust the data coming from the TOYOCOM unit.

Further, I set up data acquisition specifically to monitor the VF1-E1 and VF2-E1 fuel trim levels.

You can see the fuel trims constantly cycling at highway speed.

I can still get 27mpg (British gallons) (10.2L per 100km) doing highway miles but around town it plummets due to the Acceleration Enhancement feature.

They key thing to note here is the ECU reserves the right to have the final say.

Give me a few moments and I'll upload some screenshots from the TOYOCOM playback files to demonstrate what I'm saying.