sc400 won't idle, timing...or something...
12-17-14, 06:36 PM
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sc400 won't idle, timing...or something...
1992 sc400
A few months ago, It developed a starting problem. It wouldn't start unless I held foot partially on the gas pedal, and I'd have to use the pedal to keep it from stalling a few seconds (hot, or cold, didn't matter. EVERY TIME I start it, I have to do that) But once it starts, it runs silky smooth at the time, I
Ran Seafoam through it
Changed ECT
Cleaned IACV
Cleaned MAF
Changed driver side Ign Coil
None of them worked.
I was pretty sure, the ECU was bad, because the Check Engine Light never came on with ignition key on, though, while driving on the freeway, it did come on, dim at first, but as you press the throttle, it gets brighter...anyways, I left it alone for a while until I could get the time and money to get the ECU rebuilt
Recently, I sent the ECU to a shop to be rebuilt, and they told me that it was in too bad shape to rebuild...ordered a rebuilt ECU on Ebay for $150.
Hooked up the "new" ECU and the engine seems to run worse than before...It won't idle at all now, and when I use the gas pedal, and take it up the RPM band, it sounds as if the engine is running on 5 cylinders or something. but this time, I can at least check the codes.
22
ECT Sensor Signal
24
IAT Sensor Signal
41
TP Sensor Signal
47
Sub TP Sensor
I've already changed the ECT sensor, so It's odd that it comes up... I removed it, and put it back in, to make sure everything was tight, pulled the ECU fuse, and it still comes back
IAT I assume is Idle Air Temp? quick forum search tells me that it's in the MAF
and does the TP codes indicate that I need to replace the sensor? or that it needs adjustment?
and...wth is a "sub TP sensor?"
This seems like waay too many codes especially since it was running so smooth with the old ECU (once it does start)
could it be one thing causing all of those codes??
I'm at a loss here...I'll spend the $150 for the TPS if I have to...but it would SUCK if it STILL doesn't work...
A few months ago, It developed a starting problem. It wouldn't start unless I held foot partially on the gas pedal, and I'd have to use the pedal to keep it from stalling a few seconds (hot, or cold, didn't matter. EVERY TIME I start it, I have to do that) But once it starts, it runs silky smooth at the time, I
Ran Seafoam through it
Changed ECT
Cleaned IACV
Cleaned MAF
Changed driver side Ign Coil
None of them worked.
I was pretty sure, the ECU was bad, because the Check Engine Light never came on with ignition key on, though, while driving on the freeway, it did come on, dim at first, but as you press the throttle, it gets brighter...anyways, I left it alone for a while until I could get the time and money to get the ECU rebuilt
Recently, I sent the ECU to a shop to be rebuilt, and they told me that it was in too bad shape to rebuild...ordered a rebuilt ECU on Ebay for $150.
Hooked up the "new" ECU and the engine seems to run worse than before...It won't idle at all now, and when I use the gas pedal, and take it up the RPM band, it sounds as if the engine is running on 5 cylinders or something. but this time, I can at least check the codes.
22
ECT Sensor Signal
24
IAT Sensor Signal
41
TP Sensor Signal
47
Sub TP Sensor
I've already changed the ECT sensor, so It's odd that it comes up... I removed it, and put it back in, to make sure everything was tight, pulled the ECU fuse, and it still comes back
IAT I assume is Idle Air Temp? quick forum search tells me that it's in the MAF
and does the TP codes indicate that I need to replace the sensor? or that it needs adjustment?
and...wth is a "sub TP sensor?"
This seems like waay too many codes especially since it was running so smooth with the old ECU (once it does start)
could it be one thing causing all of those codes??
I'm at a loss here...I'll spend the $150 for the TPS if I have to...but it would SUCK if it STILL doesn't work...
12-20-14, 02:49 PM
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I changed the other coil which did nothing so far as I could tell.
Pulled the IACV and cleaned it again...there wasn't any carbon build up or anything, but when I put it back in, it idles pretty roughly, but it does idle now...but only with the MAF unplugged. I guess maybe pulling the IAC apart and putting it back together loosened it up *shrugs*
With MAF plugged in, it won't stay running even if I hold the gas pedal.
Sounds like a bad MAF?
Pulled the IACV and cleaned it again...there wasn't any carbon build up or anything, but when I put it back in, it idles pretty roughly, but it does idle now...but only with the MAF unplugged. I guess maybe pulling the IAC apart and putting it back together loosened it up *shrugs*
With MAF plugged in, it won't stay running even if I hold the gas pedal.
Sounds like a bad MAF?
01-16-15, 03:17 PM
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Okay, I've left it for a while and came back to it this morning when I got a replacement MAF in the mail. Changed it, and it's still misfiring and backfiring badly I think it's a little improvement, but that may be placebo effect...
Both of the ignition coils are new, but I unplugged the passenger side, and it made no difference to the idle. Then I unplugged the drivers side, and it was way worse. Wouldn't idle at all...
The tune up is still pretty fresh, but lat time, I used the cheapest plugs/wires I could find. I'll pull the plugs and take a look at them tomorrow and do another tune up with higher quality parts...and see what I can find...
It's a little disappointing that no one seems to want to help me out on this forum, but hopefully when I figure it out, it'll help someone else searching for a solution...
Both of the ignition coils are new, but I unplugged the passenger side, and it made no difference to the idle. Then I unplugged the drivers side, and it was way worse. Wouldn't idle at all...
The tune up is still pretty fresh, but lat time, I used the cheapest plugs/wires I could find. I'll pull the plugs and take a look at them tomorrow and do another tune up with higher quality parts...and see what I can find...
It's a little disappointing that no one seems to want to help me out on this forum, but hopefully when I figure it out, it'll help someone else searching for a solution...
01-16-15, 04:06 PM
#6
With the replacement ECU, did you: a) confirm matching part numbers, and b) make sure they used the proper capacitors in the repairs? I agree with your thinking that the ECU is a likely culprit with that many CELs, but running worse after the swap suggests that the "new" ECU has its own issues.
I assume TP is Throttle Position Sensor, so Sub TP would be the TRAC TPS alongside it? You can buy low mileage sensors for under $30 (each) for those two.
I assume TP is Throttle Position Sensor, so Sub TP would be the TRAC TPS alongside it? You can buy low mileage sensors for under $30 (each) for those two.
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03-13-17, 10:02 PM
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95 Lexus SC400 1uz Fe idling problem
Okay guys been battling a problem with my 95 Lexus SC400 for a long time now the car would run rough would not idle unless you kept your foot on the gas I replaced idle air control valve mass air flow sensor EGR valve EGR temperature sensor cam sensors crankshaft sensor spark plugs wires nothing seemed to fix the problem even replaced all the plugs to All Those sensors what it ended up being was the throttle position sensor so if you ever have a problem like mine more unlikely it's going to be the throttle position sensor oh and also I replace the fuel pump control module behind the driver side seat it's in a panel up underneath the driver side back seat window but all it was was a throttle position sensor
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