I noticed the other day that my 89 Toyota Pickup was knocking a little under load. The sticker under the hood said to jump two termindals on the diagnostic connector and set the timing to 5DBTC. I did this (timing was at about 16-17DBTC), but I couldn’t get the timing any further back than 6DBTDC before the distributor hits a stop. However, at this setting, truck was very slow and got poor fuel mileage. So I set the timing to where it runs good and doesn’t knock.-- about 13DBTDC.
So what seems to be the problem is that with the two terminals jumped, the timing isn’t changing at idle like it’s supposed to. Brief searching online suggests that this happens when the TPS isn’t telling the computer that the throttle is closed, but also supposedly when this happens the Engine Light comes on solid. Mine blinks the “everything’s okay” code when the terminals are jumped.
So the truck seems to be working fine now, so I’m not too worried about this, but I’m still curious about why this might be happenening. Any ideas?