almanai

Hi all
This is my first post and I am new member
I have 1998 ls400 and i hope you will help me ...
Here i aam going to describe ...
First.
When shifting from N to D RPM will drop to 300 rpm and it will roun rough .
What i have done.
1-Cleaned the throttle body (I replaced 5 nos. of throttle body ) but did not solved the problem
2- Cleaned the AMF sensor ( 2 nos replaced) still the same problem
3- Checked for vacuum leake and did not found any leak.
I need you help pls.
Second
Check engine light on...pulled the code ( P0172 / System too rich bank1)
What i have doe.
1- ckd MAF sensor and cleaned it
2- ckd fuel pressue regulator was working properly.
3- ckd vacuum leak and found PCV Hose was broken so i replaced the hose with new one along with new PCV valve
and the ligh did not come a gain.
but there is an other issue
car seems to misfire or hesitation / loss power or cutt off under heavy load and/or when acceleration.
Note- Now there is no any code on the dash.

I am waiting for your reply and advice
Thank you ...

AFLS400

I had similiar problems (low idle and P0172 code. I also cleaned the TB and MAF and it cleared up the problem for a week and came back. I changed my coolant temperature sensor (looked like the original) and all my problems when away. It has been about 3 weeks now and everything is fine with the added bonus of improved gas mileage (20-21 mpg in the city).

almanai

The ECT Sensor replaced with new one but still the same problem
Any help gys.?

Yamae

Try resetting the ECU disconnecting the battery negative cable for 15 minutes.
Since you replaced the broken PCV hose, the ECU at least needs to relearn the new air flow conditions. The real trouble shooting will start after that if nothing changes by that.

RA40

iTrader: (6)

Miles/km on car?

almanai

(The real trouble shooting will start after that if nothing changes by that)
Can you pls give more details / Explanation

And i will reset the ECU to see what will happen then.

Yamae

There are several possibilities and those can't be written simply by my limited English. One of the typical problems is the clogged air mix/assist path which doesn't show any code. The detail is here below but all in Japanese.
http://blogs.yahoo.co.jp/ks1106spiderman/1099329.html

Anyway I will wait for your feedback including miles/km and the past your maintenances. I also need to know how the car has been running before you notice the problem. Was it started all of the sudden or step by step?

Dylroberts

My 2000 has the same issue, I brought it my mechanic about the hesitation and the rough gear changes and they told me I had a faulty TPS (Throttle position sensor). Maybe check that? I plan on getting that fixed within the next week.

Yamae

Do you get any code?
If not, clean the throttle body and the air mix path before replacing the TPS.
The cleaning doesn't cost too much. This also improves the gear shift problem in a situation like turning a corner speeding down and then accelerate. If your car doesn't accelerate well for a few to several seconds after turning, you should definitely need to clean those. The link below helps you visually.
https://www.clublexus.com/forums/ls4...ml#post8164859

Another issue regarding the rough gear change, the ECU capacitors sometimes cause the problem for models after 98.
https://www.clublexus.com/forums/ls4...ml#post8173285

almanai

Hi Every one
Sorry for late reply…
My 1998 ls400 it has 200k mils.
Again I will describe the problem, Actually the car is start fine and the RPM during cold time (Morning) is 1000 rpm and when it reach the normal operating temperature the RPM drop to 700 rpm in ( P OR N ) once I am shifting from N to D The RPM drops to 300 rpm and idling rough ( Car does not move unless I give little gas ) , But when shifting from N to R idling is normal.
Also I notice when I shifting to D and switch A/C or Lights RPM will raise to 400 rpm.
Maintenance History
1- Transmission oil and filter replaced.
2- Engine oil and filter replaced.
3-Vacuum leak checked and all hoses are ok.
4- Throttle body cleaned / (Question: How to clean Air mix path? And during cleaning it should I stop the engine or clean it during engine is idling? )
5- AMF sensor cleaned and replaced with new one.
6- ECT sensor replaced with new one.
7- Spark plugs replaced / Coils checked one by one and all are ok.
8- PCV replaced with new one along with new hose.
9- Fuel pump checked and it is working properly / Also fuel filter checked and replaced with new one.
10- Fuel pressure regulator checked and replaced .
11- Fuel injectors checked and cleaned also.
Now the car still idling rough when shifting from N to D .
Can this issue related to ECU OR transmission problem?
Note- The car was running normal before this issue occurred and it happened in one time for rough idling .
Pls I need your help to fix this issue
Thank you all.

Yamae

Did you read the code other than P0172 lately?
If you still have P0172 code, I worry about a stuck injector.

almanai

Hi and thank you for your reply
There is no any code and already the error for p0172 code fixed by replaced PCV valve and hse


Hi Every one
Sorry for late reply…
My 1998 ls400 it has 200k mils.
Again I will describe the problem, Actually the car is start fine and the RPM during cold time (Morning) is 1000 rpm and when it reach the normal operating temperature the RPM drop to 700 rpm in ( P OR N ) once I am shifting from N to D The RPM drops to 300 rpm and idling rough ( Car does not move unless I give little gas ) , But when shifting from N to R idling is normal.
Also I notice when I shifting to D and switch A/C or Lights RPM will raise to 400 rpm.
Maintenance History
1- Transmission oil and filter replaced.
2- Engine oil and filter replaced.
3-Vacuum leak checked and all hoses are ok.
4- Throttle body cleaned / (Question: How to clean Air mix path? And during cleaning it should I stop the engine or clean it during engine is idling? )
5- AMF sensor cleaned and replaced with new one.
6- ECT sensor replaced with new one.
7- Spark plugs replaced / Coils checked one by one and all are ok.
8- PCV replaced with new one along with new hose.
9- Fuel pump checked and it is working properly / Also fuel filter checked and replaced with new one.
10- Fuel pressure regulator checked and replaced .
11- Fuel injectors checked and cleaned also.
Now the car still idling rough when shifting from N to D .
Can this issue related to ECU OR transmission problem?
Note- The car was running normal before this issue occurred and it happened in one time for rough idling .
Pls I need your help to fix this issue
Thank you all.

Yamae

The air mix/assist path has 2 bigger holes and 8 smaller holes. After removing the lid unscrewing 2 Philips screws, clean all those holes especially 2 larger holes first spraying a can of cleaning solvent while your engine is idling to 1400 rpm (up and down). Don't rev too much. The engine rpm tends to drop and you need to control the throttle cable not to stop the engine also change the rpm between 750-1400rpm in order to change the condition.

Usually you need a whole can or 2 because clogged path can't be cleaned easily. Sometimes you need to try again in a week or after 300 miles run. If still not OK, you need to visit a dealer / a professional shop and ask them to clean the injectors including the air mix/assist path.

almanai

[QUOTE=Yamae;8771491]The air mix/assist path has 2 bigger holes and 8 smaller holes. After removing the lid unscrewing 2 Philips screws, clean all those holes especially 2 larger holes first spraying a can of cleaning solvent while your engine is idling to 1400 rpm (up and down). Don't rev too much. The engine rpm tends to drop and you need to control the throttle cable not to stop the engine also change the rpm between 750-1400rpm in order to change the condition.
What you mean ? Give me more an explanation? Please step by step
your engine is idling to 1400 rpm (up and down). Don't rev too much. The engine rpm tends to drop and you need to control the throttle cable not to stop the engine also change the rpm between 750-1400rpm in order to change the condition.

Should I stop the engine while cleaning the air mix path or clean it during engine is runing?

Should I take the throttle body out before i clean air mix path?

NOTE:- All 8 injectors are cleaned before one month ago .

Yamae

I feel that you are not a DIY oriented person.
Regarding your 2 questions, the answer lies in my explanation. Read it again carefully please. I still have difficulties understanding English but you must have more.

Regarding the injectors, a 98-00 has different ones from regular injectors. The conventional cleaning can't clean the air mix path because it is an independent path and is isolated from the path from the fuel pump. The regular cleaning machine only cleans the path from the injector, you must understand.