MattLS400

Good day folks, after having executed a Diagnostic on my 1996 Celsior (UCF21) with a 1UZ-FE engine, no trouble codes are appearing.


FIRST START on a morning (engine is cold) --- The vehicle works beastly perfect in traffic and on highway. No smoke, no rough idling. Normal Idle at 900 RPM

After 20 minutes (when the engine is warm) ----The vehicle begins to rough idle.
------------------------------------------------------------When in traffic/ while cruising or lightly accelerating roughly between 1200 - 1900 RPM the engine will buck, and the RPM will dip down to 200 RPM, then resumes to its normal operation idle of 700. Sometimes the RPM dips so low, below 200 RPM that the engine shuts off....

-------------------------------------------------------------When driving on highway (80 Kmph and more) which is above 2000 RPM on the Tachometer, the vehicle does not rough idle, it runs smooth. However, If I am driving slowly on the highway (approximately between the 1200- 1900 RPM) the rough idle and jerking would persist.



POINTS TO NOTE
Mileage-- 120, 000, and stopped there since,
The Speed-O-Meter has stopped working.
The temperature never reaches above half level, it’s always either half or below the half level.

I have changed the following;

all 8 injectors to new injectors 23250-50020
Oil
Engine Crankshaft Sensor changed to new DENSO 90919-05002
Fuel Filter inside of the fuel-tank to new 23300-50060
8 Spark Plugs changed to Platinum DENSO Spark Plugs

UPDATE : Parts changed after having taken the advice on this thread and other threads as at 7/02/2014 .

Engine Coolant Temperature Sensor
2 Ignition Coils
Fuel Pump inside of the Gas Tank
jumper wire or "direct" run from terminals 3 and 4 in the fuel pump relay
IACV serviced
Pre-Cat O2 Sensors changed
M.A.F meter changed
Spark Plug Wires changed
Other ECU plugged in
2 Distributor Caps Changed
2 Rotors Changed
1996 IACV changed to 1994 IACV - Black smoke ceased.

Nonetheless the problem still persists. Any assistance would be more than greatly appreciated.

LScowboyLS

my vote is failing ECU capacitors - very common known defect in 1994 models! (actually 92-97 are particularly plagued but any year LS400 can have this issue, and you have several of the key symptoms, some of which are: no codes, speedo not working, rough idle, shutting off, etc.

but first I would replace the following:

gauge temp sensor with the genuine Toyota part
engine coolant temp sensor with the genuine Toyota part

these can only be purchased at a Lexus or Toyota dealership, but some dealerships sell online at around 25% discount

these two sensors are located right beside each other right behind the passenger side coil, kind of under the plug wire tray, a little behind it

the temp gauge should never go higher than halfway unless the car is overheating!

deanshark

Personally I would suspect the ECT Engine Coolant Temp sensor.
https://www.clublexus.com/forums/ls4...ange-pics.html

MattLS400

thanks for your response guys. But question, wouldn't a faulty ECT sensor show up on the diagnostic ?

According to this link, at least,

http://www.carsdirect.com/car-repair...erature-sensor


Remember I indicated that no sensors are showing up ? But should I proceed to change this sensor, how can I test the resistance of this sensor ?

deanshark

It wont always set a code when it is bad, actually most dont. With your car being a 94 I am willing to bet that if, or when, you do change it that when you put a socket on and twist, the top half would probably snap right off. It's 20 yrs old, they deteriorate. Plus, it's the most important sensor you have on the car. I could never figure out why they dont have it as regular maintanence.
Some people, including myself, have used the one from Autozone b/c it's cheaper but with the money you already spent you might want to get OEM, your choice.

LScowboyLS

Exactly why, on my car, it will always be replaced with the real Toyota part!

steve2006

The fuel filter on a 1994 should be external inline located around the driver's side rear wheel arch area?
The workshop manual does show the testing proceedure for the temperature sensors but you still have to remove them to do the tests, as already mentioned they probably won't survive removal so just replace them with OEM ones.
For the other problem see post 2.

MattLS400

thanks. Does anyone have a part number for this ECT sensor ?
What can explain my speed-o-meter not working ? furthermore, the total mileage on my LS400 has stopped recording.

LScowboyLS

ECT sensor is Toyota p/n 89422-20010

speedo could be needle sticking, but more likely is failing ECU capacitors

MattLS400

So i had my electrician check out my ECU....all capacitors are fine...the same problem is still occuring :/

deanshark

Did you change the ECT yet? It's worth the money b/c being as old as it is there's a 99% chance it's bad anyway. (should be part of regular tune-up) When you say your speedometer isn't working do you mean the needles dont move, (speedo and tach) or it's not lit up? Sticky needles is a common problem with the LS.
Mine stick when it gets humid and I need to bang on the top for them to move or when I drive about 40 MPH it will unstick.

LScowboyLS

would be curious as to his methodology for checking these capacitors, as this is beyond the scope of most anyone with the schematic being unavailable from Denso - even the dealership does not know how to "check the capacitors"

the capacitors do not necessarily have a visual failure when they go bad

Yamae once showed a complex electrical engineering way of checking the capacitors via ripple analysis, but there are very few people in America who would know how to do this, so I am thinking this was not done.


yes, did you?


we need to do a systematic approach here, you only know the car is getting too hot if you also know the gauge sensor is correct!


what appears to be a mechanical sticking of the needles can also be symptom of the failing ECU caps!

MattLS400

ok guys, lets start with clarifying the speedo not working....


when I say my Speedometer isn't working, I mean that the Speedometer needle is not moving at all. As well as the mileage is not increasing, meaning its stuck 120,000. However, The Tachometer needle is working fine along with every other gauge on the dashboard. Furthermore, they are all lit up...

Lavrishevo

iTrader: (1)

Speedometer failure combined no mileage increase is failed speed sensor at the transmission. Correct me if I am wrong.

Yamae

The speedometer is not directly driven by the speed sensor. There is an ECU in between them. The signal from the speed sensor is sent to the ECU and processed. The ECU uses the processed signal to control the AT and others. The speedometer is just one of those others.

When the speed sensor is failed, there happens not only no movement of the speedometer but also many other problems such as no mileage increase, the AT doesn't shift properly, the gas mileage calculation fails and etc.

So there might be a possibility that the speed sensor is OK but the ECU is not fully OK.