Austin2048

Hello, I'm new here. Picked up this SC400 recently and I've been having some trouble getting it to run right. She has a rough idle and sputters a lot during acceleration and also bucks a lot when decelerating or keeping at a constant speed (the lower the speed, the worse the bucking). It's also a lot worse when the motor is warmed up vs it being stone cold. So far I've replaced the Spark plugs, Distributor caps, and both ignition rotors. I have a hunch that the issue I'm having might be caused by either bad plug wires, a bad coil or two, or clogged cats (which I'm hopefully cutting out within the next week or two).

The other day the CEL kept going on and off. I pulled code 71 (EGR). Then earlier today I was driving it and the CEL stayed on solid so I pulled codes again. This time I got codes 13, 31, and 71. I pulled the EFI fuse to reset the codes, took her for a drive for a few minutes, CEL came on as soon as I started it. But this time its only throwing a code 13. The 31 and 71 are no longer showing up. I took a video to try and show what I'm talking about. Sorry if anything is coming out unclear. I've been up for the last 36 hours. If you have any questions that would help further troubleshoot this, ask away. I'd love to get this car running great by the end of the month So I can let my girl drive my Camry so she can start school.

t2d2

iTrader: (8)

The CEL codes could very well make it a different scenario, but the rough idle, sputtering, and bucking sounds similar enough to the problems I was just working on that I would recommend checking your TPS and throttle set screw. I haven't tested long enough to be positive the issue has been eliminated (the gremlins in these cars seem to resurface after a day or two, just after you think you got it nailed down), but so far that has done the trick.

https://www.clublexus.com/forums/per...dle-1uzfe.html
https://www.clublexus.com/forums/per...on-issues.html

RedMansSC3

iTrader: (3)

My sc300 would run fine, then at random times and rpms would give me some wierd sputters and bogging. Changed out that fuel filter. Fixed that problem. I know this doesnt have anything to do with your codes, but another cheap maintenance thing to check.

t2d2

iTrader: (8)

My personal experience: DO NOT change the fuel filter unless you're convinced it's necessary. Mine was an absolute nightmare that required patching in new fuel lines to salvage. I later discovered that my fuel gauge reads 4 gallons low, so I was bathing in 6 gallons of gas that never stopped flowing and I had extensive burn marks for a few weeks. Not fun. A couple days ago, I saw that Toyota considers it a lifetime maintenance-free item. How that's possible, I don't know, but I still had the old filter (presumably factory, given the impenetrable thread sealant goop that's also on the fittings in the engine bay) so I blew through it, and air passed through freely.

Changing the filter had no effect and there's no indication that the old one actually needed changing. Mechanics recommend changing them every 6-12 months, but the car companies disagree for some reason. I suppose that's similar to oil change intervals, where most of us subscribe to the 3,000 mile interval we've grown up knowing, rather than the 6,000+ stuff listed by manufacturers.

Joey-E

iTrader: (1)

Check your ignition coils common problem with age.

Austin2048

Thank you for the helpful input everyone. Ill get around to checking everything sometime this week. Its hard to do anything during the week while working 3rd shift. Ill try setting the tps, ill test the coils, and for the hell of it ill check the resistance of the plug wires. I just don't know why this code 13 is still there when all the other codes went away on their own.

I did hear that about the fuel filters. I read an article about the mk3 supra fuel filter and how its designed to last 1 million miles. I guess Toyota is using the same type of fuel filter on more than just the mk3 supras.

Also, I have one other question. I noticed this when checking codes but when I turn the key into the "on" position the fuel pump is continuously running where as in my Camry when I turn the key to "on" I hear the pump come on for a few seconds and shut off. The previous owner did mention something about bypassing some relay or something with the fuel pump. Would that cause this?

SC400slide

iTrader: (11)

Code 13 is RPM signal, so it sounds like it might be your ignition coils if idle is rough. I had the same issue as you, directly at 40 MPH the thing would buck and surge like crazy, replaced the TPS and set it to spec, still wasnt perfect but it helped, the issue was bad o2 sensors. Go ahead and swap those out...it's kinda pricey to do but they probably need it anyways if the previous owner let the car get like this.

Good luck

Austin2048

Is there a way to test the o2 sensors? Ill be checking out the coils soon but they aren't too expensive online. The previous owner didn't do a damn thing with it. He bought it and it was running like crap. He just tried different sensors and a different used tps and the fuel pump thing. He gave up and was gonna part it out but I bought it since it has a clean title.

If I'm driving 35-55 MPH I have to turn over drive off, 20-35 I drop it down to second or else it bucks bad. It runs with almost no issues if its kept at a steady high rpm with very easy acceration. Doesn't buck much if I'm cruising at 70.

t2d2

iTrader: (8)

https://www.clublexus.com/forums/8591911-post24.html

"Also about the o2's if yours were really bad that could affect it. you mentioned resetting it and it drove well, did it drive really well? if so you can also disconnect the plugs for the main o2's and reset again. this time the car will not learn off the bad o2's. if the problem does not repeat you prob need to change your o2's and at 182k its likely time to do so anyways. these have a service interval of around 100k give or take, so its up to you to check everything the previous owner simply skipped doing, which is often alot on sc400's.
I don't know the specific part number but its best to look at your old one. its either a 2 bolt type or a screw on type, and then count the number of wires. knowing those 2 things you can easily order the denso universal replacement for it, or you can use the model or vin number to get the real plug and play part."

Austin2048

Ok, so I haven't had much time to check much but I did check the resistance of a couple spark plug wires. I've never used a multi meter to check resistance so I'm not sure if these numbers are in check or if I even had my multi meter on the right setting. I tested the number 1 and 7 wires. The number 1 wire gave me a reading of 04.4 and the number 7 wire gave me a reading of 08.4. I read that the resistance should be no more than 25k. I had my multi meter on the 200k setting. Does that mean those 2 wires have a resistance of 44k and 84k?

DTrizzle

My 300 did almost the same thing and it was the ecu. I replaced nearly every sensor before I figured that out. I picked one up used from a guy here under $100.

t2d2

iTrader: (8)

Did your ECU show signs of old age, i.e. leaking capacitors, or did it simply stop functioning correctly?

DTrizzle

I never cracked it open tbh. Im pretty sure mine got wet though so I never investigated it.

t2d2

iTrader: (8)

I'm guessing you don't still have it? I'd love to know if there are examples of ECU failure without the typical visible signs of deterioration.

Austin2048

Before I check the ecu I want to look more into the code 13. Its rpm signal #2. I haven't had time to dig into it much. I checked the timing over the weekend and its spot on. Also tried 3 different afm's and tps's. The timing belt isn't cracked or anything but it does look a little worn. The junkyard around here has a couple 1st gen LS400's. Those ecu's would be compatible with the SC400 right?