This will be my introduction I suppose....

Wife is considering taking her parents' 03 LS430. LONG story... but they both passed almost two years ago... and the wife thought taking the car into our care for our daughter (possibly) to drive later on would be nice.

Well. It has issues. Some that are simple maintenance stuff (brakes/suspension, etc).
We went out to look the car over this afternoon and I found it to be in worse shape than I recalled. The warning triangle light lit up and flashing, ESC OFF lit and "CHECK VSC" on display. Seems like the throttle is only responsive through the idle circuit. Absolute no load throttle in neutral is 2200 RPM and its a slow rev. Idle is high at 1100. Goes into gear and shifts through all gears, but there is practically no throttle response. I was able to limp it home at a slow 30-50mph depending on terrain.

With some internet searching, the "parts cannon crowd" seems to say the throttle body is bad.
I put a OBD2 app to it and got a P2102 code.TAC motor circuit low. I cleared the code and it came right back.
I can see both accelerator pedal sensors on the app and they both respond at the same rate throughout pedal travel.
Throttle blade position is dead flat. I pulled the intake tube off and pushed the throttle blade open manually, and the app showed a response on the monitor relative to how much I opened the bade manually.

I put a power probe on the throttle motor and was able to electrically open the throttle blade that way.
I started to try to test out the harness from the TB to the ECU... but got a surprise.
I had my multimeter set to continuity (tone) and as I was plugging one probe into the TB harness (whiteish wire), the tone went off. I looked down and saw that the other probe was laying on the metal tab that secures the ECU in its box. Tested both wires on the TB side and both gave tone to ... essentially the chassis of the ECU. In my experience, that shouldn't be.

I admit I have a lack of experience with Lexus/Toyota, but I'm not sure where to go from here.
I tried to isolate the TB harness wires at the ECU, however I get a weak continuity tone across all three wires next to each other on the same plug.
In this case, it would be the first plug nearest the front bumper. The plug and port on ECU look to be in perfect shape, so melted plug or short inside the plug is not likely. I currently have no shop manual for this car and no access to a wiring schematic.

I have read that the ECUs can require repair from specialty shops.... but I'd also like to hear of anyone's personal experience with this. Particularly if you have had to use an ECU repair shop.

 

Fiddled with it a little more this evening after work. So here is what I've come to so far.

I pulled the ECM and had a look at the board. There is NOTHING obvious like I've seen on youtube and other sites which show the leaky capacitors. The board looks good.
Tediously probed until I identified both wires for the throttle motor. Good continuity on both.
Power probed the wire at the ECM and again got a positive result with the throttle body. So, no harness short that I can find.

Started the car up again, still no pedal response... just that slow rev to 2100 with a high idle of 1100 RPM.

Figured I'd try some throttle calibration stuff I've seen work on other makes just for giggles... no luck.

Then I figured what the heck, I'll just pin the gas pedal and turn the key.
BAM. Full rev. (engine was already warm... so relax... it's not a mustang)
Great throttle response as I revved the engine, but as soon as I let it drop to idle, it started the high idle with slow climb to 2200 again.

Restarted the car with the throttle pinned again to get the RPM up and kept it at about 3,000 for afew seconds and paid attention to the dash. Ob course it dinged and all the VSC lights came on again.... but the engine was still responding normally to throttle inputs...... uunnntil I let it drop to idle again. Same crap.


So, now I'm not really sure where to go with this crap. Still leaning towards ECM.....


In addition, the car has sounded like it has a misfire since I started it up yesterday.
I did confirm that the front left cylinder is dead... unplugged the #2, and the engine lugged. Reconnected that one and disconnected the #1 .... zero change.
Its not the coil, as I swapped 1&2 and got the same result on 1. Either the plug (which looks new), the harness or the injector..... oorrrr it could be the ECM.


Again.
If anyone has any experience with similar issues, I'd love to hear it.

 

i dont know anything about testing the wiring, but before you go too deep - a weak battery (low voltage) can cause all kinds of issues, including the CHECK VSC lights. Make sure your battery is a solid 12v+

 

I have a 2001 and been a member here since 2004 and I think this is the first time I have heard of this problem here. This car is very dependent on a good voltage at startup and immediately after starter stops for the ecu. With an ageing battery my car would start fine and sometimes not go into reverse properly. Waited until mirrors opened and telescoping wheel completed then start and all well. Measured battery voltage to diagnose this. Changed battery and never had problem again. Suggestion here if not already tried is disconnect battery and completely charge and hook back up and immediately crank. This computer gets confused when low voltage initially.

 

the battery is good I think.
we jumped it off initially, but after that it sat for two whole days on a battery charger. Static voltage was a solid 12.1 when I checked it 30 minutes after taking it off of the charger. Still at 12 after three starts and some idle time. Alternator is hovering around 13.9-14.1 from what I was seeing.

Last night while I was looking at the ECM the battery was disconnected for almost an hour.

 

if you had to jump the battery , its not good.. these cars are extremely sensitive to low voltage. I have to replace my battery every 2-3 years on the LS430, and make sure you get the biggest strongest highest quality battery that will fit

 

I'll pull it and take it to be load tested.
The battery is less than a year old. Will see where that goes.

 

On a side note, I had already reached out to more than one ECM repair shop. I ended up speaking to a tech on the phone. Said he has heard of this type of fault happening, but not on this early of a car. He said it has happened on later model cars, and that the fault was found to be in the chip... which they classify as an unrepairable fault. So far, I've had a response from a second shop, but the rep hasn't emailed me back yet with my explanation on the symptoms yet.

 

Voltage after charging and waiting 20 minutes is supposed to be 12.7 volts. The battery may not be your problem but could be or heavy parasitic drain bringing it down. The low voltage of 12.1 after a charge is a problem. This is a good sign in that it could very well be a voltage problem. don't worry about load testing it as 12.1 volts 30 min after charging is either a bad battery or large drain.

 

 

As far as I know, this may be the 2nd report about the symptom of a failing TPA. The first one was this.
https://www.clublexus.com/forums/ls-...l#post11608129

Something like this

video

may happen too.

 

Excellent info and a good read.
Not sure this is an issue with mine. The throttle plate moves freely and responds very quickly to voltage when applied directly. I might go down this road if I have to. Thank you for sharing that link. I'll have it on my radar.

 

So, the thing is... I have tried to cause new codes intentionally. I've unplugged two additional coil packs to force a misfire code, and this thing will not register any more codes other than the P2102 that is stuck in the computer. It will not clear. You can absolutely hear there is a dead cylinder on this car... at least one... it sounds horrible. Cylinder 1 is dead. Only thing left to test is the fuel injector for that, but that is another path in this web of troubleshooting.


Video is for you to see, the throttle body works. But only if I pin the pedal and start the car. Keeping the throttle above idle even after the warning lights all come back on it still works. Until it drops to idle. Then stops working.

 

If you clear all the codes and start the car with the accelerator floored like you did are all the warning lights gone until back to idle? The way car starts it is not a battery issue.

 

I get the same result every time.
clearing the code and then NOT starting the car…. The code remains and the lights stay lit as you see.