95 Era SC400 erattic idle, and sub o2 censor codes

[LT_Chambers]

Hi all,

I have a 1UZ out of a 95 SC400 in my Supra, but I'm having trouble, it has an erratic idle from 800-1200 and doesn't seem to want to stop. I have pulled codes, and only got ones for the sub o2 sensors, witch is a given because I do not have them. I cleaned the ivsc and lubricated it (it was gunked up), that didn't solve it, then I attempted to remove the MAF, it held a unhealthy but steady idle, it was around 500 rpms. Could it be at fault and not throw any codes? Also, could no sub o2 sensors cause a erratic idle? I don't see how though. Thanks!

 

[stevechumo]

If this is a swap, then perhaps some swap experts can jump on this. However, there're still some basics on the car. The car will throw the check engine light if you don't plug the 02 sensors in. I'm not sure if it can cause the erratic idle, but it can because the ECU can't see the feedback, so it may throw more of less fuel to the engine. That can really cause the bad idle. I never tried to unplug one, so I can't tell for sure.

Unplugging the MAF can only make it worse. I unplugged the MAF on my SC one time and the fuel was dumped so much into the engine to the point that it stalled.

 

[sideshow]

sub o2s should make no difference
they are there to should a code if the cat converter gets blocked

remove the isc and wind it about half way in so u get say a medium idle
bolt it back up but dont plug the eletrical connector to it
run engine see if idle moves up and down again
with it unplugged then it cant be isc causing idle to change
u could even get long nose pliers and gently crimp the hose feeding air to the idle motor
crimp it till idle steadies
if it still doesnt steady then its prob not isc

if it has done this from when u first got the engine running in yr supra it could be something wired up wrong

did u drive the 1uz when it was in the sc400

 

[LT_Chambers]

Ahh, some good info!! I will try this tomorrow, well today, haha (12:04 AM). I did try some other parts, switched out the MAF, and switched through a couple of TPSs, and the problem still persisted. Even sprayed starting fluid around vac lines to check for vac leaks and there were no signs of a vac leak. So my plans are to try to eliminate the ISC as the problem, I have to keep narrowing down the possibilities until a solution is found.

As for history on the engine, I picked up the engine/tranny after it was out of the car. Guy had it for a swap into his SC300, he planned to twin turbo it. So I never got a chance to hear it run. Not my best move, I wouldn't normally do that, but for the price I got it for, I couldn't turn it down.

As for wiring, I'm pretty confident in my wiring, used a Lexus wiring book to do the wiring, and the engine only really needs about 7 wires to get power to everything and make it run.

Thanks for the help, its much appreciated!!!

 

[sideshow]

yes the good old 7 wire hook up
well i hope u used an efi relay and a fuel pump relay
and yr fuel pump doesnt run all the time with ignition on so when u have a crash yr fuel pump keeps going and yr burn to death hehehe

i think most of here knows what i feel about 7 wire hookup heheheh

anyway i cant help much if u recon u only need 7 wires for everything to work properly

maybe just look at yr diagrams and see everything has power aswell
yr efi relays needs to be controlled by ecu too

if u can isolate isc from rest of enigne se eif it still plays up

 

[LT_Chambers]

Yea, I really don't think I only need 7 wires to make it run. I thoroughly went through every required dash/engine bay connector, hand wrote the pin number and color of the wire, and had a short description of what it was a part of. I even made diagrams. I then scoured the local auto yards and found both a Supra and a SC and scabbed the plugs to make "swap harness" so if anything had to change, the 1UZ/Supra harness would remain intact. All though, in my initial set up, I was not supplying power to all of the components(missed two wires in the dash side) I reverted back to the 7 wire "hook up" as a guide just to get the car to run. I will double check my wiring and see if its all ok.

This is really just a troubleshooting kind of thing, I will try to eliminate the ISC as a problem, first see if its getting power, then see if its the problem, then modulate the air incoming to it. I have talked to the guys in Florida with quite a few 1UZ - Supra swaps going on and two of them had a similar problem, one turn out to be a vac leak, other needed a new ECU (would only surge when warm).

Here is a link to a video of whats its doing: http://www.youtube.com/watch?v=BNv-eKfnVcM

Anyway, I really appreciate the help. Since I started cruising the Lexus forums it seems that no one knows anything or doesn't want to help, but that's why I like this forum.

 

[zen]

yes but its better not to chip in with info if ones just guessing..quite a few do..that just confusses things..

anyway, this may be a blessing ....once you have found the fault your understanding of this engine and ecu will be much greater and you will know if your wiring is good..i hope you soldered everything..

 

[LT_Chambers]

Yea I understand, I wont post much at all unless I'm positive of what I'm saying.

I think this was a good learning experience, I can now help others who run into the same problems. Mainly because I did find the problem, the idle speed controler valve was stuck wide open, and seems like it had been for quite some time. Found a used one localy and the idle held.

First I tested it, un pluged it,and it held an idle, but then started to surge just as before. Pluged it back in, and then "pinched" the supply to it and the idle started cruising like it should, about 750 rpms.

As for my wiring, the heavier gauge wires and ECU power wires were all soldered then heat shirnked, and the ligher guage stuff was just heat strinked, but thoes wires are mainly just for guages and some other simple stuff.

Thanks for your imput, and thanks for the advice. I have currently put about 90 miles on the new set up in the Supra, only had a couple of hicups, but its been quite fun!

 

[jibbby]

Can someone tell me what and where the ISC is? I have a high idle after a timing belt change and a 94 transmission swap.. It revs high almost 1000rmps, the then bouces when I lay off the gas rolling at highway speeds.. I'm wondering if the trans codes are different on a 92 because I installed a 94 trasmission into a 92 SC400 and ECU.. It's just weird.. The idle is high but holds steady..

I'm gonna mess with it tomorrow and see what I can find... Just don't know what the ISC is?

A little help would be most appreciated... I forgot how to work on this car almost it's been so long..

 

[stevechumo]

John,
Do you mean the IAC (Idle Air Control) valve? If yes, then it's the black plastic housing right in front of the upper intake manifold. It also has a 3/4" tube connecting to the intake pipe. Changing the timing belt shouldn't have anything to do with this or the TPS. I hope the timing wasn't off and advanced a little.

 

[sideshow]

hey lt i hope u soldere dthe smaller ligher wires too
not sure what u mean by jus theatshrink

anyway about 1 in 4 toyota engines i do which have a 6 wire idle control motor have problems with idle motor they are called isc or iac or isac as u can see there are many names for it

if anyone has idle probs best thing is to remove and clean and relube idle motor
sometimes this helps also these are gettign hard to find
in afew years time they will be very hard to get 2nd hand and i think in 5 years time
we should be looking at a newer style engine are steer away form the 1uz
where my shop is they are jap importers and the 1uz stuff is getting hard to find

hey jibby gbox change should not affect things if everything plugged straight in
id be mroe worried about timing belt being 1 tooth out as its very easy to do
does the engine feel as strong and do u have a code 13

anyway if u removed battery terminals off battery means u reset ecu
so take it for good drive on the highway or freeway
idle motor winds itself in and out when the revs are over 1500 or so for more than afew minutes so a good drive on the highway for 10 minutes helps the ecu find the highs and lows of the idle motor adjustment