Ls400 Engine Misses And Stutters

[bodywise]

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

[ko90ls]

what octane fuel do you use and why are you going into 26-2800 rpm's, drive with the ectpwr on? how many miles, abuse, etc? need more info. sound's like a tune-up to me, when was this last done?

[SKperformance]

What parts have been replaced from diagnosis

also other preventative maintance done in the past 24 months

[VBdenny]

Dump a bottle of Valoline Complete Fuel System Cleaner in the tank. It will cost you about $10 a bottle and I would put in 2 then fill it up. Worst case scenario is that you are out $20 and have a clean fuel system.

[cardona6569]

Change the air filter if extremely dirty, if not just clean it, second and very important, CLEAN THE MASS AIFFLOW SENSOR, THERE IS A TUTORIAL IN THE SITE ON HOW TO DO IT. SECOND FIX THAT DISPLAY IN ORDER TO SEE CODES OR WARNINGS IN THE CAR. THE MASS AIRFLOW IS AFTER THE AIR FILTER. USE ELECTRONIC PARTS CLEANER, LOOK IN THE TUTORIAL OR GO TO:

http://www.lexls.com/sitemap/

with that done if the problem continues you have some other issues. Need to have all other maintenance in up to date, like plugs, cables, fuel filter air filter changed.

C. PR

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

[bodywise]

what octane fuel do you use and why are you going into 26-2800 rpm's, drive with the ectpwr on? how many miles, abuse, etc? need more info. sound's like a tune-up to me, when was this last done?

As mentioned, this only occurs during brief time after it is warmed up. I am using 89 octane, not 91. I tried 91 and it did not make any difference. It has 200,000 miles on it. I have taken to a very saavy mechanic who traced all of this and concluded it was the ECU computer.

Dump a bottle of Valoline Complete Fuel System Cleaner in the tank. It will cost you about $10 a bottle and I would put in 2 then fill it up. Worst case scenario is that you are out $20 and have a clean fuel system.

Tried that more than once. No change. Did not make any difference.

Is this in the fuel line, fuel filter, fuel injectors, oxygen sensors. My latest mechanic checked almost all of these and found that there was a duplication of all systems leading to the conclusion it was a ECU failure.

Change the air filter if extremely dirty, if not just clean it, second and very important, CLEAN THE MASS AIFFLOW SENSOR, THERE IS A TUTORIAL IN THE SITE ON HOW TO DO IT. SECOND FIX THAT DISPLAY IN ORDER TO SEE CODES OR WARNINGS IN THE CAR. THE MASS AIRFLOW IS AFTER THE AIR FILTER. USE ELECTRONIC PARTS CLEANER, LOOK IN THE TUTORIAL OR GO TO:

<a href="http://www.lexls.com/sitemap/" target="_blank">http://www.lexls.com/sitemap/</a>

with that done if the problem continues you have some other issues. Need to have all other maintenance in up to date, like plugs, cables, fuel filter air filter changed.

C. PR

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

The mass air flow sensor. Not sure of this one. But one of the connections to the air intake IS defective. It had to be glued back again and seems tight, but when unconnecting this, the problem does definitely become much worse. I am not certain precisely what this tiny plastic connector is called.

Fixing the top (climate control) display, as you all know, is not simple. This is a daunting task unless I want to take to the dealer or to Mikado Technology to have the screen replaced. Apparently this is a common problem with earlier Lexus models.

thanks

[kyleh]

what octane fuel do you use and why are you going into 26-2800 rpm's, drive with the ectpwr on? how many miles, abuse, etc? need more info. sound's like a tune-up to me, when was this last done?

As mentioned, this only occurs during brief time after it is warmed up. I am using 89 octane, not 91. I tried 91 and it did not make any difference. It has 200,000 miles on it. I have taken to a very saavy mechanic who traced all of this and concluded it was the ECU computer.

Dump a bottle of Valoline Complete Fuel System Cleaner in the tank. It will cost you about $10 a bottle and I would put in 2 then fill it up. Worst case scenario is that you are out $20 and have a clean fuel system.

Tried that more than once. No change. Did not make any difference.

Is this in the fuel line, fuel filter, fuel injectors, oxygen sensors. My latest mechanic checked almost all of these and found that there was a duplication of all systems leading to the conclusion it was a ECU failure.

Change the air filter if extremely dirty, if not just clean it, second and very important, CLEAN THE MASS AIFFLOW SENSOR, THERE IS A TUTORIAL IN THE SITE ON HOW TO DO IT. SECOND FIX THAT DISPLAY IN ORDER TO SEE CODES OR WARNINGS IN THE CAR. THE MASS AIRFLOW IS AFTER THE AIR FILTER. USE ELECTRONIC PARTS CLEANER, LOOK IN THE TUTORIAL OR GO TO:

<a href="http://www.lexls.com/sitemap/" target="_blank">http://www.lexls.com/sitemap/</a>

with that done if the problem continues you have some other issues. Need to have all other maintenance in up to date, like plugs, cables, fuel filter air filter changed.

C. PR

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

The mass air flow sensor. Not sure of this one. But one of the connections to the air intake IS defective. It had to be glued back again and seems tight, but when unconnecting this, the problem does definitely become much worse. I am not certain precisely what this tiny plastic connector is called.

Fixing the top (climate control) display, as you all know, is not simple. This is a daunting task unless I want to take to the dealer or to Mikado Technology to have the screen replaced. Apparently this is a common problem with earlier Lexus models.

thanks

Did you ever get your problem resolved? I have a 1990 ls that has the same problem. It has new plugs, wires, rotors, cleaned the injectors, ran GM top end engine cleaner through it. It still has a rough idle and a misfire at highway speeds. It is not like a dead cylinder, but more like a random misfire. If you nail the accelerator it will run fine up to 100mph, but at steady speed you can feel the miss.

Any ideas?

[93ls400walt]

The O2 sensors function different at different engine temps. I would look at this.

[cardona6569]

Hi:

I would also replace the ignotion coils, they must be going bad by this mileage and time, and could be the cause of the problem, it shold be electrical since your prlblem comes and goes, it looks like and electrical electronic problem.

C.PR

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

[SKperformance]

if it starts at a certain distance i would lean to a sensor issue . It would have to be a sensor that is not used when the engine is cold only warm-hot.

MAF, is used all the time not temp related

o2 and egr are bypassed when cold from inaccurate readings

There are way more but i am tired and can't think

[GURUDEV]

what octane fuel do you use and why are you going into 26-2800 rpm's, drive with the ectpwr on? how many miles, abuse, etc? need more info. sound's like a tune-up to me, when was this last done?

As mentioned, this only occurs during brief time after it is warmed up. I am using 89 octane, not 91. I tried 91 and it did not make any difference. It has 200,000 miles on it. I have taken to a very saavy mechanic who traced all of this and concluded it was the ECU computer.

Dump a bottle of Valoline Complete Fuel System Cleaner in the tank. It will cost you about $10 a bottle and I would put in 2 then fill it up. Worst case scenario is that you are out $20 and have a clean fuel system.

Tried that more than once. No change. Did not make any difference.

Is this in the fuel line, fuel filter, fuel injectors, oxygen sensors. My latest mechanic checked almost all of these and found that there was a duplication of all systems leading to the conclusion it was a ECU failure.

Change the air filter if extremely dirty, if not just clean it, second and very important, CLEAN THE MASS AIFFLOW SENSOR, THERE IS A TUTORIAL IN THE SITE ON HOW TO DO IT. SECOND FIX THAT DISPLAY IN ORDER TO SEE CODES OR WARNINGS IN THE CAR. THE MASS AIRFLOW IS AFTER THE AIR FILTER. USE ELECTRONIC PARTS CLEANER, LOOK IN THE TUTORIAL OR GO TO:

<a href="http://www.lexls.com/sitemap/" target="_blank">http://www.lexls.com/sitemap/</a>

with that done if the problem continues you have some other issues. Need to have all other maintenance in up to date, like plugs, cables, fuel filter air filter changed.

C. PR

I have a problem that may sound simple but is driving me nuts. I have a very smart mechanic but I don't think he knows either.

1991 LS400 starts fine and runs fine until it warms up. Then almost on target after about 3-5 miles, it starts missing and stuttering badly, usually at about 2600-2800 rpm and while accelerating. Once it is fully warmed up at about 8 miles it runs fine again. It never runs well after 75-80 mph.

My mechanic says he has run all diagnostics and it looks like a computer failure. I know this sounds unlikely. Then I realized that my upper display panel has not been operative for the last 4 years so any engine display codes cannot be seen or displayed anyway.

I can't tell if this is eletrical, fuel, injectors or somethings else.

thanks.

:)

The mass air flow sensor. Not sure of this one. But one of the connections to the air intake IS defective. It had to be glued back again and seems tight, but when unconnecting this, the problem does definitely become much worse. I am not certain precisely what this tiny plastic connector is called.

Fixing the top (climate control) display, as you all know, is not simple. This is a daunting task unless I want to take to the dealer or to Mikado Technology to have the screen replaced. Apparently this is a common problem with earlier Lexus models.

thanks

Did you ever get your problem resolved? I have a 1990 ls that has the same problem. It has new plugs, wires, rotors, cleaned the injectors, ran GM top end engine cleaner through it. It still has a rough idle and a misfire at highway speeds. It is not like a dead cylinder, but more like a random misfire. If you nail the accelerator it will run fine up to 100mph, but at steady speed you can feel the miss.

Any ideas?

Gurudev Sept 12 2006

I have similar problem I want to share my experience, problem is not resolved.

Car would start than will sudenly stop.took to dealer reapair shop,change mass air flow. Same problem persisted. Dealer repair shop now says I should consider to change computer,as it sends wrong message,when it warms up.I have decided not to repair until i get assurace that it will take care of problem.

Hope someone may have answer for this problem !

[LScott400]

To try and confirm a computer problem, you could pull the ECM and open it up to look for leaking capacitors. This Link has pictures and explanations, but it is NOT for an LS400. I had leaking capacitors in my '94.

There are rebuilders that you can ship to with an explanation of symptoms that can test and rebuild for you.

If your diagnosis and MAF replacement were performed by a Lexus dealer and they did not correct your problem, it should be up to them to confirm that an ECM will actually fix the car. Then there should be an adjustment made for the repair that did not correct the condition since they gave the diagnosis.

[GURUDEV]

To try and confirm a computer problem, you could pull the ECM and open it up to look for leaking capacitors. This Link has pictures and explanations, but it is NOT for an LS400. I had leaking capacitors in my '94.

There are rebuilders that you can ship to with an explanation of symptoms that can test and rebuild for you.

If your diagnosis and MAF replacement were performed by a Lexus dealer and they did not correct your problem, it should be up to them to confirm that an ECM will actually fix the car. Then there should be an adjustment made for the repair that did not correct the condition since they gave the diagnosis.

Thanks LScott400. :)