xzen73x

So my '90 3vze (Auto trans) is having troubles.

Idle is stumbly, it takes a bit of cranking to get it to start when it's warm.

I have an air/fuel ratio meter mounted to the dash, so i know a bit more.

WHen i cold start it, it runs rich for about 5 minutes, and then idles normal, but it still chugs a bit. When i first step on the gas from a stop, the air spikes and i bog out for a second or two, and then it goes back to normal mixture, until the trans shifts into second, and then it goes to a rich mixture for about 5 minutes. After that, it's more or less normal, but you can still smell it's running rich in the exhaust.

I'm also being thrown code 12. I've been doing some researching on it, and i came up with

open or short in NE circuit
open or short in the STA circuit
or the ECM

Problem being i have no idea what either of those circuits are, where to find them, or how to test them (Electrical noobie). I tried digging, but nobody really explains it.

Any insight would be greatly appreciated.

oldblue

could be a bad distributor, giving a bad signal to ignitor. a lab scope is the only real way to check the signal that i know of. pull the distributor cap and see if there is any excessive play on the rotor shaft indicating worn bearings maybe.

Gamefreakgc

First things first. These engines have a "Cold Start Injector" which sprays extra fuel to ensure the engine starts in "cold" conditions. When the ECT and the IAT both record temperatures under a specific threshold, it triggers the ECU to run the injector. If only one give the reading or if both are over the threshold, it does not run. So the fact that you are reading a rich condition until the engine warms up is completely normal. That means that your ECT, IAT and ECU are all functioning perfectly in those regards.

After warming up though, you should not be switching between lean and rich conditions. The O2 sensor should adjust in a fraction of a second, not over several seconds or minutes like you are describing. I am wondering, do you have a wide-band O2 sensor on? It is a universal one or specifically for these trucks? However, fixing the CEL light might clear up the whole deal and not worry about the O2.

A code 12 is:

• Open or short in NE, G circuit
• Distributor (it's broken)
• Open or short in STA circuit
• ECM

This page will help you understand what those circuits are:

http://personal.utulsa.edu/~nathan-b.../9systemci.pdf

So basically, either the wires NE or G are damaged or broken (visual check to confirm, use a voltmeter to check) or the wire STA is broken, or the distributor is shot, or the ECM (ECU computer) is shot. ECU's rarely go bad. Distributors are obvious when they are failing, they will be like what oldblue described, or just all rusty inside like mine was. Usually though when they fail, it's a total failure and you're dead in the water.

We can't tell you what is exactly causing the issue, you'll have to investigate. But there is a problem, and that CEL (and possibly the rough driving) will not go away until it is fixed.

xzen73x

I tried pulling the cold start injector and it did nothing. Thanks a lot for that diagram though. I'm gonna have to learn how to read it Lol. I'm not very good with wiring.

The o2 sensor is also new, so I doubt it's that

I'm gonna poke around and see what's up

bone collector

http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf
it is most likely a bad distributor.

here are the steps for the tests you will need to test.
http://personal.utulsa.edu/~nathan-b...86troubles.pdf

xzen73x

I've been looking for that FSM for ages, thanks.

So it looks like i'm going to be tracing ALOT of wiring...

Any tips to make this easier on me? Lol

xzen73x

So i traced the STA wire from the ECU side, and from the Starter until it joined up with the main bunch of wires from the ECU, and i didn't find anything. I didn't follow it back to the ECM because the stock harness hasn't been opened, and It didn't seem like something would go wrong in there.



I did find that though. THe distributor has 6 wires coming out of it, and 3 are spliced into one, which does to the connector, which has 4 wires coming from it.

Think that might have anything to do with it?

bone collector

Houston we have found the problem. That is a hillbilly fix if I have ever seen one.

bone collector

I should add that the 88-92 distributors are the same. From 93-95 they changed the plug. Find a replacement. Junkyard would be the cheapest. Take a voltmeter and test it per the FSM before you buy it. I wonder if that is even a Toyota distributor

xzen73x

It must've been from a later-year truck, because i bought a new cap/rotor for the truck, and it fit right on. If the plug changed, the previous owner might have just said screw it, and done that.

I'm not sure how to check the voltage on it though. I guess i'll keep researching.

bone collector

in this picture you can see the plug on my 94 3vze distributor. the plug is a single row of 4. there are NO wires coming out of the distributor itself. the plug is molded into the body of the distributor. The only wires are on the harness side of the plug. This is why I wondered if that was even a Toyota distributor.

http://personal.utulsa.edu/~nathan-b...12onvehicl.pdf
In this link, the last page will tell you how to test the distributor.

guzzirik

What???

razor420

I have a 1994 toyota 4runner. as of just recently it started to rough idle when im in drive and foots on the brake. It comes and goes, sometimes idles rougher than other times. Usually when the cat has been warmed up and driven. when in park you cant tell anything is wrong except for a small possible hickup. I dont feel any power loss or hesitation when driving and no check engine light has come on. Any possible solutions would help, My funds are limited aswell. Thank you

bone collector

https://www.yotatech.com/forums/f116...iagram-274913/

read this. the important stuff is in the middle. Mud Hippy is basically a 3vze Guru. pay attention to what he says.

xzen73x

Thanks for the help. It was a misfire in cyl 5. Compression is 75, and 120-140 on everything else.

Sounds like I have some work ahead of me. Would that be the reason I'm getting a code 12? Or should I still replace the distributor.

MudHippy

No, that shouldn't cause any codes.

You could also check the starter relay and COR to see if both of those are working properly. Since they're both part of the STA circuit. And not thoroughly covered in the basic troubleshooting procedures.
http://personal.utulsa.edu/~nathan-b.../2starterr.pdf
http://personal.utulsa.edu/~nathan-b...96circuito.pdf

And there's no reason to replace the distributor without verifying that there's actually problem with it. And/or without verifying that the code isn't caused by something other than it.