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The '98 Model Year is when VVTi was introduced, along with a host of other changes resulting in the UCF2x Post Minor Change LS400s.
The confusion stems from the way some countries register cars. For example, an early 98 model year car sold in '97 in AUS is registered as a '97 car, rather than by model year.
Originally Posted by Amskeptic
I read from the original post that his was a 1996.
The original poster was, the poster I was replying to however (lexus_ls) has a '99.
I read from the original post that his was a 1996.
Other than that,
Superfast1 wrote:
Which does not address in any way the low idle complaint of the original poster. It is so off-the-mark for this complaint that it looks like a copy/paste from some other thread, and I recommend against this modification for any reason but ATF ending up in the intake tract or a sudden leak that ends up on the alternator.
The Idle-Up Valve on the power steering pump only adds a little additional air to the engine based solely on power steering fluid pressure ******* down the engine at full-lock. It does not help "during hard braking" or "under load (in gears)".
Factory idle speed above ambient 50*F is 650 +/- 50 rpm.
Below ambient 50*F it is 800 +/- 50 rpm
In order of likelihood from the factory manual, a low idle speed can be caused by:
1) water temperature sensor
2) ISC valve
3) horrible-but-true, the neutral safety switch. The NSW terminal is normally a ground path for the ECU in P and N, when it is not a ground path (in R D 2 1) the ECU changes the idle speed program and the mixture
4) EGR valve
5) Fuel system circuit (we have a two stage fuel pump pressure)
6) Injector circuit - another way of saying to be cognizant of a cylinder that is not firing fully due to restricted injector spray
If original then water temperature sensor should be changed in any LS400.
Am interested in your comment on Neutral Safety Switch...had a really low idle situation with stalling in Drive happen only once...This applies to what years LS400s? 1999?
If original then water temperature sensor should be changed in any LS400.
Am interested in your comment on Neutral Safety Switch...had a really low idle situation with stalling in Drive happen only once...This applies to what years LS400s? 1999?
1999 LS400 dispensed with EGR
I am extremely limited with my "knowledge base" as I have experience only with first generation LS400s. Thus, my list of possible causes includes EGR for the earlier cars.
Colin
Hello, LS400Eddo and Lexus_LS .... regarding the mysterious low idle situation, I wonder if I may share with you my latest discovery : what if your ECM / ECU was rebuilt by a guy who does a lot of Lexus ECM's ... the twist is, he only uses replacement parts that are truly sourced from Japan ... plus he has soldering down to a science .... I was surprised to find all the comments from people that he has done work for ... all is found on his FaceBook page. So if you go to FaceBook, just type in this name : Japanese ECU ECM PCM Repair by Lscowboyls ... As for me, I have an old 95 LS400 and although I am not having drivability issues, once I found out how much your car's performance can be improved with this particular ECM rebuild ... well ... gosh, I think I will for sure give it a shot : ) Read though his FB pages and you will see what I mean ... really amazing comments left by people that I bet will resonate with you. I plan on having him rebuild my unit soon .....
take care and best of luck .. .. .. .. ( I will let you know how it goes after I get my ECU done )
Hi JetCat. I actually had my ECU rebuilt hoping it would solve my low idle issue and it didn't do a thing. No change. My ECU looked great too, but I replaced all the chips.
I have low RPM and vibration because when start my car in the morning RPM go to 1200-1300 RPM
but when engine is warm and I put the car in drive ( Drive) RPM drop to 400 RPM.
if I turn the light on RPM go up to 600 in (Drive)
if I turn AC on RPM go to 600 in (Drive)
my problem is when in (D) , and AC and light is off, RPM always 400, Also, when I put the car in N or P and press gas pedal to 1000 rpm car vibrate more, but no vibration when it is below or above 1000 rpm .
There is no engine light or any warning light.
I have clean the throttle body 3 times, but I didn’t disconnect it from the car, also I cleaned the two big holes and the other small hols two times. There is no change for my low RPM.
I have change engine temperature sensor OEM part, and there is no change.
I replaced air control valve and nothing happened.
I have replaced spark plugs two times, no change for my RPM.
I replaced all ignition coil boots. Just the boots.
I have replace transmission fluid, motor mounts, and transmission mount but RPM still 400
I have replaced fuel filter , clean MAF sensor 3 times
and changed the air filter 2 times
my RPM still same when car is warmed in drive is 400 RPM
I have checked all vacuum lines and there is no leak.
Replaced radiator, thermostat, heater valve
timing belt and water pump.
I will change transmission fluid and filter next month, I was thinking maybe if I change the transsmition filter the RPM will go up becuse of a sludge or something in the filter, I don’t know.
I’m lost and I don’t know what I should do.
I inspect my alternator and battary and they are good.
Also, I’m thinking maybe the problem in fuel injector, but I have put fuel treatment in gas tank 4 times and no improvement.
my problem is when in (D) , and AC and light is off, RPM always 400, Also, when I put the car in N or P and press gas pedal to 1000 rpm car vibrate more, but no vibration when it is below or above 1000 rpm .
There is no engine light or any warning light.
I have clean the throttle body 3 times, but I didn’t disconnect it from the car, also I cleaned the two big holes and the other small hols two times. There is no change for my low RPM.
Also, I’m thinking maybe the problem in fuel injector, but I have put fuel treatment in gas tank 4 times and no improvement.
Sounds like your injector's lower part is badly clogged. The Lower part means the path for the air to go through indicated by arrows. In order to clean the paths of 8, you need to use at least a can of carbon cleaner and a compressor applying to those 2 larger holes that are connected to 8 injectors air mix paths.
Depending on the clogging level, you sometimes need to clean injectors professionally using a ultra sonic cleaning machine. I also must add that any fuel treatment is not effective to clean those air mix paths because there goes only the air not the gasoline.
The drawing below may help you to know how 2 larger holes are connected to 8 injectors to send air. Sorry that non related parts are explained only in Japanese.
Hello, LS400Eddo and Lexus_LS .... regarding the mysterious low idle situation, I wonder if I may share with you my latest discovery : what if your ECM / ECU was rebuilt by a guy who does a lot of Lexus ECM's ... the twist is, he only uses replacement parts that are truly sourced from Japan ... plus he has soldering down to a science .... I was surprised to find all the comments from people that he has done work for ... all is found on his FaceBook page. So if you go to FaceBook, just type in this name : Japanese ECU ECM PCM Repair by Lscowboyls ... As for me, I have an old 95 LS400 and although I am not having drivability issues, once I found out how much your car's performance can be improved with this particular ECM rebuild ... well ... gosh, I think I will for sure give it a shot : ) Read though his FB pages and you will see what I mean ... really amazing comments left by people that I bet will resonate with you. I plan on having him rebuild my unit soon .....
take care and best of luck .. .. .. .. ( I will let you know how it goes after I get my ECU done )
He's just another rebuilder except he's built up this mysterious aura and attempts to claim that he himself discovered the issue. He attempts to build the image that he and only he can "properly" rebuild the ECU, this is simply not the case.
LS400 ECUs have been repaired by countless automotive electricians for more than 20 years, there isn't any particular reason to pay extra for LSCowBoyLS's services. Search this forum for more information on his history, his rep isn't the best.
Originally Posted by Scraape
both my 98 & 99 have PS Air Control Valves. Or maybe i'm missing your point
We're discussing the idle air control valve found on '89-97 LS400s, not the PS idle up valve tha is found on ALL LS400s. Completely different functions.
The drawing below may help you to know how 2 larger holes are connected to 8 injectors to send air. Sorry that non related parts are explained only in Japanese.
Thank you Yamae
I’m going to clean these two paths and also I’ll clean all the injectors. However, today I found out there is a little PS leak, but didn’t drop into ground so I’m going to fix this first. I will order the seals kits.
I’ll report back once I cleaned the injector and the air paths.
I’m going to clean these two paths and also I’ll clean all the injectors. However, today I found out there is a little PS leak, but didn’t drop into ground so I’m going to fix this first. I will order the seals kits.
I’ll report back once I cleaned the injector and the air paths.
The drawing below may help you to know how 2 larger holes are connected to 8 injectors to send air. Sorry that non related parts are explained only in Japanese.
Yamae- Looks like the upper intake you're showing is the 98 & up so does the older one also have these larger air holes? I can't quite picture what the air mix path from the fuel injector's cross-sectioned diagram you showed above. When you mentioned using the carbon cleaner to clean the fuel injectors, are you talking about cleaning them while they're still attached or with them removed from the engine? Both of my 97 & 00 LS400's are in tip top shape but I'm curious so please elaborate on that. Thanks.
Yamae- Looks like the upper intake you're showing is the 98 & up so does the older one also have these larger air holes? I can't quite picture what the air mix path is for from the fuel injector's cross-sectioned diagram you showed above. When you mentioned using the carbon cleaner to clean the fuel injectors, are you talking about cleaning them while they're still attached or with them removed from the engine? Both of my 97 & 00 LS400's are in tip top shape but I'm curious so please elaborate on that. Thanks.
I believe he is referring to cleaning the air mix path with carbon cleaner, because it's essentially connected to the vacuum part of the injectors. Injectors wouldn't need to be removed unless they're really bad.
I don't think your 97 has an air mix path, but your 00 definitely does
03-19-18, 02:30 AM
