Hey, I have a 1990 Toyota 4runner 3vze. 130k miles on it, bought it used and it is obvious it was sitting around for a long time. Bad rust, interior leaks, etc.

Engine ran fine when purchased, but then started shaking badly at idle. Vibration goes through the body while in drive, less so in park. Shortly after that it started losing power on any sort of hill. Tested it on a steep hill and it dropped down to 12mph. Even small inclines it needs a lot of gas and time to get up to speed.

I've changed the fuel filter, replaced the spark plugs, replaced the distributor cap, put seafoam in the gas tank. Haven't changed the plug wires yet.

Pulled up a CEL code 12, which apparently is:

Open or short in NE, G circuit
Distributor
Open or short in STA circuit
ECM

From what I can gather so far, the NE and G circuits run from the distributor to the ECM. I couldn't find what the STA circuit was. I've read about people testing the NE, G wires as well as the Distributor with a multimeter, but I don't know how to go about this or what readings I am looking for. Any specifics on how to do this or other advice on why it is running this way would be appreciated, thanks.

 

Bad TPS?

 

STA is the STArt circuit.

Here's the FSM for the distributor: http://web.archive.org/web/201212070...12onvehicl.pdf Remember that your problem is in the circuit, not necessarily the distributor. Make sure your wiring is free of obvious defects.

Shaking at idle is often caused by missing. You can diagnose that by pulling the spark plug leads one at a time; the one that doesn't change anything isn't working.

You should check for spark AT the plug. The sensible way to do this is with the inductive pickup of your timing light (if the light flashes, the wire is connected to a firing plug). A timing light is about $30, and you need one anyway.

Good luck!

 

So I pulled the plug wires out of the distributor while it was running one at a time. 3 and 4 made no difference, while the rest slowed the engine down. I could visibly see sparks jumping from the distributor to the ends of the spark plug wires when they were held close together, even on numbers 3 and 4. I replaced all the plug wires which made no difference.

I'm considering taking the intake manifold off next to check the fuel injectors. Apparently when you do this you need to replace the gaskets on the manifold, which is about 100$.

As the engine was fine when I purchased it but had been sitting for a long time, and then got worse after driving it a little, I'm wondering if there was a bunch of gunk in the fuel tank that clogged those 2 injectors after being driven for the first time in a while. I already put one round of sea foam in the tank which didn't do anything (in fact I lost power not long after that), so I don't know if more injector cleaners will help or not.

Now that I know that 2 cylinders aren't firing and I saw sparks going from the distributor cap, should I still be chasing after this CEL code? Or maybe it is a second, unrelated issue?

Oh, I also did a compression test and it seemed to check out fine.

 

If you have spark coming out of the distributor to 3&4, and there's no change when you pull the wires off the distributor, I would pull those two plugs. They could be clogged up, damaged somehow, maybe got broken by and over-enthusiastic installer, etc etc. Try swapping them with 1&2, for example, if they aren't visibly failed, and see if the failed cylinders follow the plugs. In other words, if you swap them, then pull their plug wires while it's running, and again, no change, but only with 1&2 now, bingo, bad plugs, without a doubt.
Always make sure that, should you replace the plugs, which might not be a bad idea in any event, you use only OEM plugs. I believe Denso K16R-U are the preferred plugs to use. Those are the regular, average, everyday, plugs. Nothing special. What Toyota would put in at the factory. The least expensive, as well.
There are variations on a theme available, though. Platinum, split electrode, etc. I understand the Rubidium bead version give the best spark strength, last the longest, and so forth. They're also the most expensive. Rare earth elements work great, but you pay for what you get, and get what you pay for.

Sometimes a drive at full speed, once the engine is good and warmed up, like a run on the freeway for a 1/2 hour, will burn gunked up plugs clean. Sometimes. No promises, though. It's just an idea.

Last, nut not least, make sure the head's ground is in good shape. Since the head gasket prevents electrical current flow from the head, through the block, to the battery, the heads need their own grounds. Usually from the head to the body someplace is used. If the head's ground isn't good, ie clean and free of corrosion at both ends, it can interfere with the spark. Weaken, or prevent it completely.

Is this any help?
Pat☺

 

I already swapped all the plugs out for new ones, no change in engine shaking or performance.

 

I seem to have found the issue. The fuel injectors are all plugged up with rust, I'm guessing from the gas tank.

 

Yep, I bet that would do it!

Well, I don't know if you can clean them out or not. Maybe a short blast of compressed air back through, from the end in the intake manifold to the end in the fuel rail, but with 12V applied to open the injector? Probably have to do it fast so you don't burn up the injector.

Otherwise, either send them out for re-work at an injector shop, or buy a new set to put in. Only other choices I see.

Make sure the fuel system is cleaned out real good, including a new fuel filter, and so on. Sounds like you'll need to drop the tank and clean it out real good, as well. Maybe even get it coated inside, or replace the tank, too. If there's rust in the injectors, it came from someplace, most likely the tank. If enough got through the filter to clog the injectors, then there's rust throughout the entire fuel system. Both the pressurized "feed" side, and the unpressurized "return" side. The Pulsation Damper, and FPR included. How badly must they be clogged up? Going to take a good deal of cleaning, and possible replacement of parts, like the FPR.

Good luck! The problem just expanded a bit
Pat☺

 

I cleaned them out by following some youtube tutorials. 2 were visibly completely plugged with rust. Put them back in and it runs perfectly now. I've swapped the fuel filter. The old one may have been the original that came with the vehicle, and was probably clogged. I'm hoping I can get away with periodically swapping the fuel filter instead of dropping the whole gas tank and cleaning it out. Maybe frequent new filters will catch the all the rust? Dropping and cleaning the tank just sounds like a pain...

Thanks for all your help!