1995 Ls400 - Idle Air Control

[nll714]

Hello to this LS400 forum -

I have a 95 LS400 with 144k miles on it. As of late, I have been experiencing some low idle speeds, but most important, it has been "conking-out" on me at complete stops. Thankfully, it starts right back up and Im on my way.

I stopped by my local service shop, described the problem, and he stated with confidence that it was an issue with the Idle Air Control Valve.....specifically with the high mileage on my car. He quoted roughly $400+/- to have it replaced. Of course, he would run a diagnostic to make certain this is the issue, but again, feels very confident that this is the root of the problem.

Ive done some looking online about this problem but wanted to come straight to the source!

If anyone could offer up if this is an relatively "easy" part to get at, as well as to clean, that would be much appreciated. Some instructions on how to get this done would also be appreciated.

I look forward to your replies.

[blake918]

This problem is probably not caused by the IACV.... http://us.lexusownersclub.com/forums/index...&hl=jerking

[nll714]

This problem is probably not caused by the IACV.... http://us.lexusownersclub.com/forums/index...&hl=jerking

I appreciate the link. However, Im completely lost about this ECM. Is this something that has to be replaced by a dealer / mechanic? Thanks for your reply.

[93ls400walt]

The ECM is located behind the glove box. It is fairly easy to get to by removing the under panel and glove box on the pass. side. If you get that far I'm sure this site can help you with the procedure.

[eatingupblacktop]

Howbout some more info. Is there any difference in the idle between a cold start and a warm start? How does your car idle at in gear fully stopped? What's the rpm? Does it fluctuate? What's the range? Do you hear any unusual sounds? Same questions for when it is in neutral? Any other driveability probs?

[nll714]

Howbout some more info. Is there any difference in the idle between a cold start and a warm start? How does your car idle at in gear fully stopped? What's the rpm? Does it fluctuate? What's the range? Do you hear any unusual sounds? Same questions for when it is in neutral? Any other driveability probs?

Man, this is awesome.....thanks for the replies. To answer your questions the best I can:

There isnt much of a difference in the idle between warm and cold starts. This problem just started occuring a couple of days ago. I'll have to start guaging that better today. I have no idea if this piece of information will help or not, but I'll include it for the hell of it:

The FIRST time this happened I had my car parked at the airport for about a day and a half. Got in and it fired right up and didnt notice anything out of the ordinary with the idle while waiting for it to warm up. Almost immediately got on the interstate from the airport and drove about 25-30 miles at about 75mph with no problems. Got off at my exit and the first traffic light that I got to is when it died out on me. Started right back up and fortunately I didnt hit another light / stop until I got home (was after 1AM).

My car idles, Im estimating, in gear fully stopped around 700-800rpm -- when "normal". Im sure there has been some fluctuation, but I havent paid attention to it closely enough to give you a precise answer....will look closer today. I do, however, notice immediately when this problem starts. I sort of feel the rpm's steadily drop down to about 200, then the car shuts off. I have never heard any unusual sounds.....NO driveability problems at all.

I have yet to guage idle rpm's in neutral but will be doing so today.

Thanks for the replies. I look forward to getting this solved soon as I hate driving around paranoid wondering if the car is going to die out at every stop....especially when I have my 2 yr. old son in the car.

[bernard 96ls400]

Make sure its not the fuel pump. Replaced mine at 140k on my 96, and also replaced it at similar mileage on my 91 years ago.

Fuel pumps WILL fail on these cars, especially if they do a lot of sitting without regular driving.

[eatingupblacktop]

There have been many reported causes for your symptoms. Everything from a weak alternator, dirty throttle body, tps, iacv, isc, and ecu. That your idle doesn't change when engine is cold or hot could indicate a prob with the cold start circuit.

The iacv does get sticky and the plunger and mating surfaces can be cleaned out. The idle speed motor bearings can dry out making it hard for the motor to adjust the idle. They can be easily and inexpensively replaced. The ecu which controls the isc motor can also be the source for your prob.

Here's an exhaustive thread you might want to read up for more info:

http://us.lexusownersclub.com/forums/index...=15699&st=0

[Marfm]

I bought a 1995 LS400 with almost 100K miles, at the beginning work normal, few days after start showing several cylinders misfiring. I check the spark plugs, one had coolant and another oil. I disassemble the engine and found that he head gaskets were bad. I had change all gaskets and seals with original Toyota parts, new injectors and wires, other than the head gaskets the engine was very clean and after the replacements the compression is at the specifications in all the cylinders. all the hoses were check and the damaged ones changed. After the repairs the engine start normal and run in that way for a couple days.

One morning when I started the engine, suddenly the idle became erratic. fluctuating from 400 rpm to 2000 rpm. . I changed the TPS with a generic one. this seams to fix the problem, but few day later the problem change to start at high rpm 1400, the transmission shift out of time and rough, lack of power and hesitation at acceleration. I change the TPS again with a original Toyota and same exact number; again, this seams to fix the problem.

Now some times when I start the motor, I know is going to work normal until next time; and if I let let it to warm-up normal will perform perfect. every time I start the engine when is warm (if I go to the store) start having the same problems; high idle at start and die when I stop. driving with both feet avoid the engine die when the car stop.

It is not engine light. no codes. I was reading that many Lexus owners have the same problems, and are many solutions (or non). I also have another 1995 LS 400 with over 230K miles and has no problems.

the next suspect is the computer, but I'm tired of working in this car and changing parts and the problem persist.

There is anybody who can give me some guidance?. will be very appreciated.

[landar]

Fredy, welcome to the forum.

If you have another 95 LS400, you could just temporarily swap the ECU's to see if that is the problem. The thread mentioned in post #8 has a lot of good suggestions. I would read that thread in detail -> http://us.lexusownersclub.com/forums/topic/15699-9596-ls400-low-idle-engine-dies-and-jerking-thre/

Also, if you turn on the AC unit, and the car does NOT stall, that suggests the ECU as well. There is apparently a programming bug in some 95 ECU algorithms. There may also be some dried-out capacitors causing problems. But I would swap your ECU's first to see if that has an effect. The ECU is located behind the glove box.

[Vegan]

You can get new capacitors at digikey website for the ecu. IACs are on ebay for $50. If your's is the kind with screws near the black connector part, you can take it apart and clean it.

ECU Info:
IMPORTANT: The capacitors may look perfectly fine and yet be bad,
they look great at first, then deteriorate and cause damage to the ECU
very quickly





MODELS/ENGINES AFFECTED:



This issue affects all Lexus & Toyota models with the following engines: 1JZ, 2JZ, 1KZ, 1UZ, 5E, 1G, 3S



The following are some of the models affected:



● Lexus LS400 - 1990-2000 (in 1997 and earlier models, the problem is extremely common)

● Lexus SC300 - 1993-2000

● Lexus SC400 - 1992-2000

● Lexus GS300 - 1993-1996



● Toyota Celica GT - 1985 -1998

● Toyota Supra Mark III (JDM) - 1986-1993

● Toyota Supra GT - 1995-1997

● Toyota Supra Mark IV - 1993-2002

● Toyota Supra Twin Turbo - 1993-2002

● Toyota MR2 - 1990-1999

● Toyota Camry - 1987-1991

● Toyota Soarer - 1992-2000

● Toyota Aristo - 1993-1996

● Toyota Celsior - 1990-2000





SYMPTOMS:



Please understand that any one of these symptoms can be a sign of ECU capacitors beginning to fail. - You do not need all or most of them to have this issue!



Your ECU capacitors are strongly suspected if you have at least one of
the following intermittent issues on your Lexus or Toyota:



● problems in getting into diagnostic mode or scanner says "no communication"

● random dropping into "limp home" mode

● weird shifting problems

● OBD port is unresponsive, seems dead

● throwing random fault codes

● engine won't rev out/rev limits at 2000 or less rpm

● engine runs like crap, then suddenly runs fine again

● random not starting or cutting out

● low idle or erratic idle

● often very hard to start, requires starting fluid

● transmission will not automatically shift, only manual shift is possible

● transmission jerks from 1st to 2nd gear, and kinda slips from 2nd to 3rd

● no A/C compressor operation

● idle speed rolling up and down, or sometimes too low and sometimes too high

● speedometer not working reliably

● speed (cruise) control not working

● tachometer not working sometimes

● air bag light flickering intermittently

● A/C going into reset with flashing front defog light (front defog light typically flashing 10 times)

● check engine light on sometimes, but no codes stored, often in concert with ECT light

● ECU not communicating with scanners or not displaying codes with jumper installed

● bad sulfur exhaust smell in concert with not running right above





I was actually experiencing several of these symptoms including ECU not wanting to communicate!



So, with no engine diagnostic codes to work with, I checked all of the
grounds, voltages and other obvious causes, and then in a MacGyver-Steve
Jobs moment of insight, I decided it must be the electrolytic
capacitors inside the ECU, which had appeared fine in an earlier inspection a few months earlier when the problems began. I suspected it was the capacitors because I discovered this problem back in the 1990's on Nissan 300ZX
and the Mitsubishi DSM models. History just keeps repeating itself! -
It was also bound to be ECU-related, because this diverse set of issues
has only on thing in common - the ECU!



sure enough, upon re-inspection, the corrosive leakage was very bad, so bad that the main circuit board
could barely be saved!, I replaced all 6 electrolytic capacitors, and
now every single problem listed above is gone! - and the engine also
seems to have more low end power than it had even before the symptoms
above appeared!



if you recognize ANY of these symptoms listed above, bad ECU capacitors are a likely culprit!



I now believe any Lexus over 12 years old would greatly benefit from
having ALL 6, 8, or 10 electrolytic capacitors in the ECU replaced with
high quality new ones! - these were not part of a defective batch, but
rather a quaternary ammonium salt capacitor issue, as explained by world-renowned ECU engineer Yamae in post #8 below. (we are very lucky to have him here at Club Lexus!)



this is NOT something a junkyard computer would solve, it is an age and
sitting up problem, a junkyard ECU would have the same issues.



IMPORTANT: It is critical that you use the exact premium Japanese
low ESR capacitors I have linked to below in the recommended capacitors
section, even if you are having someone else do the work, the
correct capacitors are very rare type and they will not have them
locally - if they use other capacitors, the repair will not solve the
problems you are having!



the power difference alone makes it worth doing, and just because an electrolytic capacitor looks good, doesn't mean it is - 93-97 LS models are showing up with this capacitor issue in particularly high numbers
and other models such as SC model are showing up in high number on even
earlier years such as 1992, this also affects the 2JZ and other Toyota
engines!



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



LET'S FIX IT!!



a new ECU would also solve the problem, those cost $2400 at the
dealership, the parts I used to make mine just like a new one are less
than $20 delivered from Digi-Key - and it is important to order from an authorized dealer of these great capacitor brands in order to avoid counterfeits - so FORGET EBAY, AMAZON, ETC.



make sure you use 105C rated low ESR caps from the 4 reputable Japanese capacitor companies Rubycon, Nippon Chemi-con, Panasonic & Nichicon







it is CRITICAL that the replacement caps be low ESR type and from one of the brands listed above - don't cheap out on your vital ECU!



WARNING - DANGER: this is not a good first-time soldering
project, the existing capacitor removal and associated desoldering,
cleaning, inspection, soldering and re-inspection is involved and is in
some very tight places, you must be experienced at soldering and pretty
good at it, or else you need to locate someone who is very experienced
at soldering, and then you should buy the special capacitors this job
requires, and then let him or her do the operation of replacing them -
the NipponDenso ECU in your LS400
is a delicate piece of very expensive electronics. If you wouldn't feel
comfortable taking apart a laptop computer and getting it back together
successfully, then you probably do not want to be doing the electronic
portion of this repair.



If you need further advice on recapping, you can post here in this thread!



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



which caps you need and how many depends on the year model of your LS400



I would advise you pull the ECU and verify the cap values before
ordering, to make sure. You can reinstall the ECU in 5 minutes (leave
the lower glove compartment out for now) and you can drive the car until
the caps arrive in the mail from DigiKey (normally just a couple of
days)



WARNING: You must use premium Japanese low-ESR capacitors for this
repair to be successful, this kind of capacitor is very rare, they do
not stock it locally, you must order it from the links below!



1990-92 LS400 needs 10 or 11 caps as follows:



Qty. 3 of 10μF - 50v

Qty. 2 of 15μF - 35v

Qty. 3 of 47μF - 63v

Qty. 2 of 100μF - 10v

Qty. 1 of 220μF - 16v





1993-94 LS400 needs 8 caps as follows:



Qty. 2 of 10μF - 50v

Qty. 2 of 15μF - 35v

Qty. 1 of 47μF - 63v

Qty. 2 of 100μF - 10v

Qty. 1 of 220μF - 16v





1995-97 LS400 needs 6 caps as follows:



Qty. 2 of 10uF - 50v

Qty. 1 of 47uF - 63v

Qty. 2 of 100uF - 10v

Qty. 1 of 220uF - 16v





1998-2000 LS400 needs 11 caps as follows:



Qty. 2 of 10μF - 50V

Qty. 3 of 47μF - 63V

Qty. 2 of 100μF - 10V

Qty. 1 of 220μF - 16V

Qty. 1 of 33μF - 35V

Qty. 1 of 47μF - 25V (special BP capacitor) - high reliability capacitor, replacement recommended but not critical

Qty. 1 of 330μF - 35V - high reliability capacitor, replacement recommended but not critical



1998 and up owners: you can replace the capacitors of your original ECU
without affecting security and the theft deterrent system, but keep in
mind that if you get another ECU say from ebay or a junkyard, it will
have to be reprogrammed by the dealership or a better locksmith before
your car will start with any ECU that is not the original one that came
with your car!



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



WARNING: You must use premium Japanese low-ESR, high temperature,
long life, high ripple rejection capacitors for this repair to be
successful, this kind of capacitor is very rare, they do not stock it
locally, you must order it from the links below!





~~~ CURRENTLY RECOMMENDED CAPACITORS: ~~~





DANGER! - Will Robinson - COUNTERFEIT capacitors are a
SERIOUS EPIDEMIC - make damn sure your capacitors come from the factory
authorized sources below, those capacitors you found a deal on, on ebay
or elsewhere online are very likely FAKES! - most premium Japanese
capacitors in the United States are shipped from three principle
distributors: Digi-Key, Mouser, and Newark Electronics. Anywhere else is likely a questionable source!



(this list is dynamic and will be updated as Yamae & I find additional good candidates and rule out others)

(recommendations are based on USA availability - the best capacitor made does us no good if it is not readily available)



the voltages specified in the recommended caps below are sometimes higher than the originals, this is a good thing!



the one to get in 10uF is the 50V Chemi-con KZE EKZE500ELL100ME07D - if sold out, use alternate factory authorized source here: EKZE500ELL100ME07D



in the 15uF - the 63V Chemi-con KZE EKZE630ELL150ME11D

also fine is the 100V Nichicon PW UPW2A150MPD



in the 33uF - the 35V Panasonic FR EEU-FR1V330

also very good is the 100V Rubycon ZLJ 100ZLJ33M8X11.5



in the 47uF - the favorite is the 100V Chemi-con KZE EKZE101ELL470MJC5S (sometimes sold out)

also very good is the 100V Panasonic FC EEU-FC2A470

also very good is the 63V Panasonic FR EEU-FR1J470B



in the 47uF special BP - the 35V Nichicon EP UEP1V470MPD

also fine is the 50V Nichicon EP UEP1H470MPD



in the 100uF - the 35V Rubycon ZLH 35ZLH100MEFC6.3X11

also very good is the 50V Panasonic FR EEU-FR1H101

also very good is the 50V Chemi-Con KZM EKZM500ELL101MHB5D



in the 220uF - very impressive is the 50V Panasonic FR EEU-FR1H221

also very good is the 50V Chemi-con KZE EKZE500ELL221MJ16S

also very good is the 50V Panasonic FM EEU-FM1H221

and the new 50V Nichicon HW is my new favorite! UHW1H221MPD



in 330uF - I recommend the 35V Rubycon ZLH 35ZLH330MEFC10X12.5

or alternatively the 35V Panasonic FC EEU-FC1V331



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



~~~>>> special thanks to world class ECU engineer Yamae from Japan <<<~~~

who got me thinking about how ECU's operate in my head, which lead to
this breakthrough! (and also thanks to TV character MacGyver, it's what
he would have done!)



no one understands Toyota ECU operation and design on Club Lexus anywhere in the same league with our special Japanese guest Yamae!



just consider him a guest expert ECU engineer from Nippon Denso, and you wouldn't be far off.





ECU removal:



always disconnect the negative battery cable before disconnecting or reconnecting an ECU

beware: there is at least one hidden bolt inside the lower glove box
behind a secret panel (not joking about this) the diagram below will
help, but it can be a little tricky to get the lower glove box out the
first time, just keep at it, and you eventually will locate all of the
fasteners









WARNING - DANGER: this is not a good first-time soldering
project, the existing capacitor removal and associated desoldering,
cleaning, inspection, soldering and re-inspection is involved and is in
some very tight places, you must be experienced at soldering and pretty
good at it, or else you need to locate someone who is very experienced
at soldering, and then you should buy the special capacitors this job
requires, and then let him or her do the operation of replacing them -
the NipponDenso ECU in your LS400
is a delicate piece of very expensive electronics. If you wouldn't feel
comfortable taking apart a laptop computer and getting it back together
successfully, then you probably do not want to be doing the electronic
portion of this repair.



I take NO responsibility for any damage you do to your ECU from any
information you obtained from this post. DO THIS AT YOUR OWN RISK!!!
If you completely hose your ECU, don't come whining to the cowboy! Nor
do I want it sent to me for repair! Untangling someone's 'handiwork' is
more frustrating than battling the original problem! If you have any
doubts about your skills, DON'T TRY THIS!! - If you do screw it up, it
is not the end of the world, just purchase the same part number ECU on ebay from a high rated (99.5%+) seller for around $125 or so and find someone to do this cap replacement job who has experience.



Also - NEVER use 'cold heat' types of soldering irons!! They
work off the principle of an ARC welder, and emit a current. This can
instantly destroy your ECU board when contact is made. If a good
soldering station is not available to you, a 40 watt solder pencil with a
standard tip on it will work fine.





STEP-BY STEP REPAIR GUIDE



if you have patience and soldering skill, it's not too difficult!



here is what I did:



CAUTION: BE VERY GENTLE with flexing the 2 or 4 gray ribbon
cables that connect the 2 mainboards - they will not tolerate rough
handling! - they will take a normal amount of flex required to open up
these boards flat for working on them, so you don't have to be a
complete scaredy-cat!



parts/tools to round up:



the ECU carefully opened up (be gentle with the ribbon cables)

the new capacitors (you did procure the ones Yamae & I specified above, right?)

rosin core solder 63/37 (Radio Shack p/n 64-015 or equivalent)

rosin solder flux (Radio Shack p/n 64-022 or CAIG DeoxIT rosin flux p/n RSF-R80-2)

40+W soldering iron or soldering station, 75W max - no soldering guns! (Radio Shack p/n 64-2071 or equivalent)

● my favorite soldering station: Hakko FX-888D

● my next favorite: Weller WES51

solder sucker (Radio Shack p/n 64-2060 or equivalent) another type that is also good is Radio Shack p/n 64-210 (some people find this a huge help, I don't use them but very rarely)

stainless steel safety pin or, if available, a stainless steel dentist's
pick is also fine of the tip is straight and sharp like a needle

nail clippers or flush cutters (Xuron 9200 or similar)

91%+ isopropyl alcohol

baking soda

vinegar

distilled water



CAUTION: - static electricity can kill an ECU - some people wear
anti-static wrist straps, but I find them a pain, here is a better plan
and what I do in my electronic's bench: all 100% cotton clothing and
bare feet!



FIRST: - take photos of what caps go where originally, plus make a DIAGRAM of cap sizes & placement!



1. - remove old caps using soldering iron
heat or desoldering iron and a simultaneous back and forth tug after
making diagram of values and placement, just keep tugging, they will
come out

2. - gently brush areas of board where caps were using toothbrush with
baking soda/water paste to remove any acid leakage residue

3. - wash area with vinegar to remove any caustic base damage

4 - inspect board copper traces to insure that they are still intact, it
is OK if they are now a brighter copper color than surrounding traces,
but severed or completely eaten away traces will require professional
repairs and you are probably better off getting another ECU from a
junkyard or ebay and replacing the caps in that one

5. - rinse board with distilled water to remove vinegar acetic acid

6. - rinse board twice with 91% isopropyl alcohol

7. - inspect desoldering job with loupe

8. - using medium large safety pin, re-make holes in desoldered pads in
board to accommodate easy installation of leads of the new caps, heat up
the solder pad, insert safety pin, let cool and the stainless safety
pin will twist right out, leaving a perfect hole for new cap leads!

9. - solder in new caps, double checking polarity (+/- orientation) -
use 63/37 rosin core solder, and get some rosin solder flux (I like
Radio Shack p/n 64-022) and cover the solder area well - slather it all
over where the new caps will be soldered - the new capacitors do not
like extended heat, just get in and get out with the soldering iron, and
make sure iron is ample wattage (like 40W+) - I do not like to apply
heat for over 3-4 seconds at one time. Use LIBERAL amounts of the
RS/CAIG rosin flux mentioned above in the parts list, this is the key to
making the soldering process behave!

10. - trim leads on reverse side of board of each installed cap with clipper

11. - rewash board with 91% or higher isopropyl alcohol

12. - inspect soldering job with loupe

13. - blow compressed air to make sure no clipped leads or stray solder
remain on board, use about 25 PSI or less, it's a circuit board, not a
crankshaft!

14. - Once ECU is reinstalled into car and everything is reconnected,
only then do you want to reconnect the negative battery terminal

15. - BEFORE cranking engine the first time, click the ignition
switch over to the RUN position for 1 minute to let the other ECU
components acquaint themselves with the new caps and let them precharge.

Read more: http://www.clublexus.com/forums/ls400/656360-all-my-crazy-lexus-issues-solved-ecu-leaking-capacitor.html#ixzz3273iykwo