Hi all. So, I was driving my ’87 4Runner (22RE) on the freeway yesterday and the CHECK ENGINE light came on. For a few minutes after that it still seemed to be running fine, but then suddenly the engine stopped running, and I had to coast to the side. After that it would turn over just as normal, but not try to actually fire up at all, so I had to have it towed home.

The next day I tried again to start it, and it started just fine and ran without the CHECK ENGINE light on for a while, but then when I upped the engine revs for just a bit the CHECK ENGINE light came on again. After that I checked for diagnostic codes, and I had a 6 (“No engine revolution sensor (Ne) signal to ECU”) and a 12 (“Knock control Sensor (KS) signal has not reached judgement level in succession”)… The information I’ve found so far (see photo) says these could be a number of things, and that the first steps would be to check for “Defective Igniter circuit” and “Defect KS circuit”. I basically have no idea how to go about checking those though, and the repair manual I have doesn’t seem to be much help. Can anyone give me a step-by-step guide to how to go about checking each of these systems, or point me at a good resource?

Of course I’m worried that in the end I might actually have to replace the computer itself. One source I found online says that actually having to replace it is rare, and that the problem is usually something else. But I’ve already had to have the computer replaced on this vehicle twice now. (Of course it’s possible that the shops that did the work weren’t being honest with me about it needing to be done, but as far as I know they were…) So related questions, if I do need to replace the computer, is there a way to be sure that's really the problem, and is that something I can actually do myself this time? And if so, does anyone know where to get a new computer? I understand they’ve gotten pretty hard to find…

Thanks for any help you can give me!

Patrick