SC93

Slide..thx for reply.

Ligit question re coil. I had strongly suspected it but got sidetracked when the 24 and 31 error
codes showed up on my manual OBD check and felt sure the MAF was the issue. The unit
I purchased was advertised to be compatible with 93 sc400.

I am at this time doing the "in the sun" heat up of the car once more and see if the poor
performance shows up again. So far I have started the car six time this morn with car in garage
and no problems at all the.Tthe engine check light remains on and every time I clear it it comes
back on and a manual jumper check brings code 31 up again ...no 24 code (new MAF installed).

I'll let the car sit out for a couple hours and do a start and see test and report back later this
eve.

Once again... if I should unplug the suspected coil and it was truly faulty, would the error code
31 disappear or would it stay and probably more error codes show up.

SC93

Slide..thx for reply.

Ligit question re coil. I had strongly suspected it but got sidetracked when the 24 and 31 error
codes showed up on my manual OBD check and felt sure the MAF was the issue. The unit
I purchased was advertised to be compatible with 93 sc400.

I am at this time doing the "in the sun" heat up of the car once more and see if the poor
performance shows up again. So far I have started the car six time this morn with car in garage
and no problems at all the.Tthe engine check light remains on and every time I clear it it comes
back on and a manual jumper check brings code 31 up again ...no 24 code (new MAF installed).

I'll let the car sit out for a couple hours and do a start and see test and report back later this
eve.

Once again... if I should unplug the suspected coil and it was truly faulty, would the error code
31 disappear or would it stay and probably more error codes show up.

====================================================================

Hey, just went outside and hood of car was hot,hot. Car is black and today's sun (Florida) is
out big time.

Started car, rpm's at 1500 level. Mashed accelerator and when rpm got to about 3800, it dropped
way down and car stalled. Repeated three more times with same result. Something is
breaking down and heat seems to be bringing it on. I am going to unplug the drivers side
coil and see what happens. Will report back later.

SC400slide

iTrader: (11)

I have always thought that the pre-95 SC's were karmen vortex AFM only, but I guess I was wrong. If it cleared your code, awesome!
EDIT: Worded this wrongly, 95 and earlier do have Karmen Vortex type AFM.


More error codes could come up, the 31 probably will stay there. If you unplug a bad coil, the car will do absolutely nothing when that part is unplugged. (Same running, idle and problems) If you were to unplug a good ignition coil, the car will run worse and perform even more poorly.

====================================================================

...which brings me to say again, I think the coil is at fault. Let us know what the outcome is! Hope it's the coil and not some melted wire in the firewall...

SC93

Slide....I just got back from happy hour ...(a couple of wines) maybe not at my quickest but ran a curiosity test.

Car at evening room temp. Unplugged drivers side coil. Car would not start. Plugged back in
and car started and could exceed 4000 rpm with no breakdown and idled normally.

Does this have any significance with regard to bad coil?? Could passengers side be bad. Where
is passenger side coil located...not visible from front view engine compartment.

Also... a bit confused re TPS ( throttle position sensor) and idle air control valve (ICV) which I have
seen pics of with gunk on the plunger and want to clean.

I see what I think is the throttle plate controller on the aluminum housing but no ICV valve which
I would expect to be in front of the TPS. Where is the ICV for a lexus 93 sc400??

SC400slide

iTrader: (11)

That means your drivers side ignition coil is good. (You probably guessed)

No, sounds like the drivers side coil is good to go for now. Passengers side could be bad. Let's hope it is.
Location of the passengers side coil: Read this thread: https://www.clublexus.com/forums/per...ack-sc400.html


The TPS that says "EFI" above it is the one that will need replacing/adjusting/whatever you're going to do with it. If you have Trac system, your engine bay will look like this one, but if not, you will have one 1 TPS.

As for your IACV, this is directly beneath the throttle body/intake manifold. Sorry for the bad pic. The empty hole is where the IACV is located on a 93 SC400.

Next on the list, test your passenger side ignition coils and go from there.

SC93

Slide.. again thx for reply'

See my attached pics. Not too good at camera work but I think u can get general idea of what
I have under hood. I have EFI and no traction on throttle body. For the life of me, can't find the
IACV. Do I have to remove the aluminum intake housing holding the throttle plate to get
acesss. My 93sc400 was bought in sept 92 so I would assume it would look as your under
hood pics u have shown.

SC93

Slide..

Guess the two wines made me blind. Your pic after further study was plainly enuf for me to
locate the valve....right in front of engine bay as also shown on my pic. Looks easy to get to
so tomorrow I will remove and clean and try to check second coil out. Boy one could get a
major migraine trying to follow explanations depicting differences between coil packs ignition
coils and all the rest. I am assuming all I have to worry about is two basic coils like the one I unplugged today.

If I ever solve this issue I think I will be qualified to open my own service garage

SC400slide

iTrader: (11)

Actually, it looks easy, but it's more of a scale to moderate. Just because there is so much stuff that needs to be removed. Those plastic spark plug covers, as well as more things. Those spark plug wire guiders will be in the way so you'll need an offset screwdriver to access the IACV screws. Careful not to strip them!!! That happens quite a lot, in rustier areas. FL isn't too rusty...

On the coils subject.

The SC does not have coil packs. That is when different wires go from one "coil" thusly, a "pack". Ali could explain better. The SC has a single wired "Ignition coil", which is the correct term for our cars. Of course, we have two.

GL on the fix.

Ali SC3

iTrader: (10)

Yes def test out the passenger side coil. sounds like your rpm's are fine though not sure you want to mess with the IACV unless you are having idle issues. SC400slide you are right all 95 and under do use the karman vortex, and that is the kind he replaced it with, its just the ones on ebay have an exposed IAT element it seems in addition to the Karman stuff. So the air temp went away but not the maf code. maybe make sure the wires on the maf connector are all the way in and secure, and that the comb in front of the maf is straight and clean. reset the ecu by pulling the battery cable or efi fuse for a few minutes.

do not shoot any cleaner into the Karman maf, you can only wipe down the honeycomb in the front and make sure it is straight and not bent out of shape. Also if you have a K&N filter you may want to swap it out for a dry one the oil over time does not help the mirror in the maf stay clean and then it cannot measure air properly.

SC93

Hang in for another confusing report:

Came home last nite...car was cold and I did left and right side coil check by disconnecting drivers side and passengers side alternately( reconnect between ea test) and car would not start in each case. Very discouraging because I was sure one or the other coil was breaking down. Car started up and ran well with both connected.

I wanted to resolve this prob on my own(with your help) but did need new plugs and serpentine belt which at moment I am not in mood to do (77 yr old with bad back) and realize plugs are not in question. So I figured at same time get another opinion to my problem and took car to local small repair shop who I trust and owner has much experience. His OBD check verified my find ...31 code. Had my old and new MAF sensors at hand and upon interchange there was no difference in car performance. He looked/checked other suspect areas which could be related to poor performance and nothing. Doesn't feel coils are problem. I mentioned ECU and he said that could be the root problem but could not verify and said I might have to go to local Toyota dealer. . major letdown and will never happen.. Anyhow I left car overnite and asked to him to do his magic and find problem.

OK...If I need a replacement ECU what part number is correct for my car. I saw on ebay a used unit for abt $100 but am confused re part number...California vs other states have same pre number different last digets....which part number is correct for me in Florida.

PS..he did take IACV out and it looked clean.

SC400slide

iTrader: (11)

Personally I try and avoid the shop completely, BUT, if the shop is trustworthy, it is probably better than encouraging back pains...Hope you get this fixed! Let us know what the problem was...that is...if the shop figures it out.

Another thing to throw out there, have you checked the fuel ECU? Not the main ECU, the fuel ECU. That might be a culprit. I actually have one for sale...
When checking the main ECU, look for leaking capacitors on the board. THe gel leaks on them overtime and if that's the case, replace or rebuild the ECU.

GL to you!

Ali SC3

iTrader: (10)

alot of people have been having similar issues lately and it is not the fuel ecu. o2 sensors and maf codes seem to come up but the car drives alright. how is your car driving now?

SC93

slide/Ali


When I mentioned that the problem was most prevalent when starting the car after it had
been exposed to the sun, he said he wanted to do the "hot car" start up himself so I left
it overnight. Will let you know his findings later today. Hopefully it will be hot and sunny
this morning for his test.

Re the fuel injection system. I did a little test myself which probably doesn't mean much. With
the car in a bad mood, I jumped the b+ and Fp terminals on the diagnostic port under the hood
and could hear the fuel pump working away quite smoothly. I had read you could actually run
the car jumped in a like manner and drive the car with resulting poor gas mileage. Would
such a test be worthwhile ..... i.e., if car ran w/o problems with fuel pump jumped wouldn't
that point to the pump ecu being faulty??

I may have him pull the main ecu and check the capacitors or I might just do it myself here at
the house. I think I am correct as to its location...passenger side right kick panel. Do I have to
remove glove box to access.

If I should follow through on the ecu check and find it suspect is 89661-24230 the correct
part number. I see California has a different number vs most ecu's...24240 I think.

Also, any recommendations where to buy. I mentioned the ebay unit at $100 but if a more
reliable source is available, please recommend. I assume any unit I decide to get would
be "plug and play" so to speak. Properly programmed and ready for use.

I'll keep you updated later today.

CatManD3W

iTrader: (18)

check out this other thread as well going on right now:

https://www.clublexus.com/forums/per...o2-sensor.html

It seems a few of us are having similart problems whether it be sc300 or sc400..

SC93

Cat..........thx for reply.

Yea, seems like a similar problem. I will know a little more re my sit when I get my car back
from a local small garage serviceman. He is normally pretty good but so far since yesterday
he can't find problem I have described in this thread and certainly do not want to go to Toyota
dealer here.

I am rather stubborn and if he can't solve problem, I will just bring it home and
continue my search for a solution. Another option I have is a local repair service that specializes
in servicing imports and has a good track record. A bit on the expensive side but less than dealer.
I may be forced in that direction if all else fails.

It is good that so many people are polite and helpful on this forum.

SC93