na4now

I need help on this one. I need this car to be right. I have alot of highway driving to do in it.

I bought this SC300 a couple weeks ago. It's a 1999, with 200k miles, ...all stock. The car is in extremely good shape. Has been been taken very good care of. No accidents, the interior is cleaner than average with no common SC interior problems, and everything looks nice under the hood, ....with all the hoses/belts in good shape, no major leaks, ect..

The check engine light has been on since I bought it. According to the previous owner, the cel is on for an o2 sensor. The engine runs great, but idles low low, at about 400-500rpm. Other than that, ..it runs smooth, quiet, and makes good power.

The exhaust smells rich, as well. Highway mileage, running 75-80mph is 17.8mpg. This is my third sc300, ...and I would usually get 21-22mpg. Hell, ..my crew cab, 7k lb. v8 turbo diesel truck, gets 22mpg highway!

I took it by the parts store today. I didnt get the actual codes. I should have. But, the guy said it was o2 sensor bank 1 sensor one, ...and bank 2 sensor one. Also, said the catylitic converter efficiency was below threshold.

I just checked, and it looks like both of the very front o2 sensors have been replaced. They look new and shiny. These are the ones, in the exhaust header, right before each converter.

So now, ..what to do? Im thinking maybe get some new, universal o2 sensors, and go ahead and change those. Even though they look new, ...I can put two brand new ones for $40. (SMP brand[DENSO 2344209] on ebay $20 shipped ea.)

But still, ...would the o2 sensors be related to the low idle? I know they have to be related to the rich smell, and poor mileage.

And, ..since these front two have already been changed, ..you think it's something else? Could it be one of the other two o2 sensors? Or, maybe the cats? Should I just go ahead and replace all four sensors? The money Ive already spent in extra fuel, ..I couldve already done all four!

JunFLR66

I wish I could offer a solution to you about the o2 sensors, I don't know too much about our cars like I do with Hondas, with Hondas if there is a check engine light on for o2 sensors it puts it into "safe mode" and automatically pulls timing so would most likely feel not as strong, fuel would likely be rich etc. just as a quick diagnostic you could pull the efi fuse under the hood for at least 10 seconds put it back in, start the car, and see if it clears the engine check. If it idles normal and runs better, when the engine check comes back on, get the codes ran and at least you will have troubleshot it somewhat.. If you're extremely lucky it may never come back on.. Don't think I helped but it's something.. best of luck

blacksc4

iTrader: (1)

since your running a 92, you can check the CEL at home with a wire jumping two pins in the port, search its a very common thread, but as for o2 causing a low idle, its possible because the 2 front o2 sensors (primary o2 sensors) read the air/fuel ratio, if it cant register it will cause an idle problem, sometime a bad ignition coil will cause this problem too, you can go ahead and change the o2 sensors that way you know theyre new and when they were changed and how good the part is, also since uve just recently got it i would ahead and do a tune up as far flushing some fluids, plugs, wires etc.
but for your problem the 2 things id check ar the o2's, coils but start by changing your plugs
also like JunFLR66 said, reset the ecu, remove the negative cable and efi fuse for a couple minutes then hook it all back up and drive around for a while, the computer just may need to relearn driving, if not the cel may or may not pop back up

1JZPWRD

iTrader: (59)

I say it's the back 02 sensors. Or clogged cats. If it smells rich then the computer is limp mode or rich. Is your trac light come at all or flash? The one next to your check engine light?

xwingzero2

iTrader: (2)

have u tried calculating the mpg yourself? or are you using the one the the sc300? If its its good mpg then its not the car its the computer.

na4now

The car is a 1999 model, ..not a 1992.

The trac light is not on.

Milaege was hand calculated. ****, ..I JUST realized that the computer does mpg! My other three SC's didnt have that!

After making this thread, I went outside, and installed a red top Optima battery that I had. Did it, just to do it. It cleared the CEL. I took it for a 30 minute ride, through Baton Rouge, and back.

It seems to have more power! I drove about 25 miles total. Opened it up, half dozen times. Ran it up to 110mph. When I got home, I killed/restarted it twice.

It still idles low, ...but the CEL hasnt come back on. I suspect it will though, huh? Certainly the previous owner didnt change the front o2 sensors, and not reset the ecu? That wouldnt make too much sense.

xwingzero2

iTrader: (2)

I dont know what else to say dude. But yay for battery! everything = more power!

abounly

iTrader: (27)

I know when my O2 went out upstream bank 1 sensor 1 it would idle horrible. I would reset the ecu, (via battery) and it would idle horribly but once the CEL came back on it idle fine. So i will assume the O2 does affect your idle.

blacksc4

iTrader: (1)

sry missed the 99 u wrote in the first post
but an o2 will 100% affect your air/fuel which will cause bad mpg and idle
im currently doing my o2 sensors, 92 sc400, had a code 25 (running lean), and i had the code week ago, reset my ecu and code was gone for a week idled low still bad mpg then it came back yesterday code 25 again, some one posted earlier with the same problem, it was his driver side ignition coil
if my o2 doesnt fix my prob thats my next step

blacksc4

iTrader: (1)

https://www.clublexus.com/forums/per...all-bad-2.html
kind of along the lines, hope that helps out