phermes1

My 95 SC400 was running fine, then last week it started idling rough and accelerating even rougher. Idling isn't so bad, but if I hit the gas, it's very rough and the acceleration isn't nearly as quick as it is normally. At first I thought it was bad gas, so I filled up with 93, then added some Lucas fuel treatment in the hopes that it would be that easy.
Then the check engine light went on. The DTC's indicate 1) a lean air/fuel mix malfunction, 2) a rich air/fuel mix malfunction and 3) A TPS issue.

Thoughts? I'm inclined to replace the TPS and see if that fixes it - however, throwing parts at a problem in the hope that it fixes it never seems to be the smartest or cheapest route.
I had a mechanic look at it and he suspects a bad coil or plug, or perhaps even a bad injector, but didn't have the tools to diagnose it better, (OBDI), and basically said he didn't want to waste my money by throwing parts at it until he fixed it.

Anyway - anyone have similar experience? If I can take an educated guess at a fix, then I'll give it a shot, otherwise I'm basically going to be forced to take it in to the dealer. Thanks in advance.

1JZPWRD

iTrader: (59)

The code DTC 25 and 26 is the trac sensor. I would adjust it a little or replacement. Easy fix. This also adjusts your idle as well. DTC 41 is the IG Power Source Circuit, which also involves the trac sensor. This is what powers the ECU and is the power for the CPU and its actuators. All of these codes leans towards the TRAC sensor, or a bad ECU. Both of these are a very high rate of failure on these SC's. I would order a new one through Carson Toyota or a vendoe on here, try the classifieds, or replace the ECU, or both. GL... Mark

phermes1

Thanks - I'm a little confused, though.The documentation I found for those DTC's indicate that 25 = lean air/fuel mix, 26 = rich air/fuel mix, and 41 = TPS. I'm not seeing anything about a trac sensor, unless that is related somehow. Clearly, this is my first time troubleshooting stuff like this.

1JZPWRD

iTrader: (59)

I understand that. I have the PDF file for the SC400. I type the codes in and wolla it tells me what it is and the symptoms that possibly could be the factor causing it. These are just some recommendations to start and the easiest would be to adjust the trac sensor, not the TPS. If you would like, I can try and email the file to you. PM me for more info, trying to help you out...

phermes1

Yes, that file sounds great. I'll PM you. Thanks for the help!

WadeLovell

iTrader: (5)

Any follow up on this? I have a similar problem on a 1993 SC300. I was driving along minding my own business today when the check engine light came on. I immediately pulled over and popped in my handy tool, The DTCs were 25 & 26 ONLY. Nothing else.

chrisindub

iTrader: (1)

My car just threw the same codes.

GS4_Fiend

iTrader: (22)

Code 25 & 26 - Car running Lean. Check MAF sensor, ECT, no vacuum leaks. Make sure car is in fuel control. Bad oxygen sensors.

Code 41 - Defective TPS. Open/Short in TPS circuit.

chrisindub

iTrader: (1)

No vacuum leaks, swapping MAF sensor doesn't change it, new O2 sensors, maybe ECU is bad? Forgive my ignorance, what's fuel control? ECT is the engine coolant temp right?

GS4_Fiend

iTrader: (22)

ECU would be the last resort so dont jump to conclusion.

Fuel control as in the PCM is in control of the fuel mixture, not too lean or not too rich.

New oxygen sensors, which ones? The main concern is Bank 1 sensor 1 and Bank 2 sensor 2. Those are the ones should be changed.

ECT is coolant temp sensor, make sure it's within specs. Make sure thermostat is working.

Dont forget to check the TPS sensor also. Test the TPS itself and the wire integrity. Search youtube there are alot of videos on how to test it. Using a meter.

chrisindub

iTrader: (1)

Changed all my o2 sensors this year up and downstream. All four.

Will check out the rest before I swap the ECU.

phermes1

Sorry folks, I should have posted the fix when all was said and done.
It turned out to be bad sparkplug wires. They were apparently REALLY bad, arcing all over the place, and causing the engine to misfire and the computer to throw funky codes. Replaced the wires and all my troubles went away.