Engine misses intermittently both at idle and throughout rpm range. Cap and rotor clean,plugs read nice light brown fuel burn color- would injector cleaner in gas help, and if not any suggestions? Thank you!
Have you changed the plug wires?
I had this problem w/my early 90’s Corolla – some noticeable missing and pinging, especially when going uphill – and it turned out to be the spark plugs. They looked ok, but the gap had increased with miles driven to close to 50% wider than spec’d. I caused this myself. I went past the recommended change-out mileage for the spark plugs. Once I put new plugs in, along with a new cap and rotor, the problem was immediately solved.
If the spark plugs are near due for replacement anyway, putting in new ones with the spec’d gap as the first step in the diagnosis is probably the way to go. I’d probably put in a new cap and rotor too while you are at it. I’m assuming changing spark plugs and cap a rotor is a fairly simple project, even for a Toyota truck. Changing spark plugs/cap/rotor on my 4 banger Corolla is a 15-20 minute job.
It’s unlikely to be a fuel injection problem unless you know you’ve had some bad gas recently. I wouldn’t put in any fuel injector cleaner. The 90’s Toyota fuel injection system is pretty much bullet proof. It would more likley be the fuel filter becoming clogged than the injectors in any event. But if it is happening at idle, it probably isn’t the fuel filter either. Look for other causes first.
mt bike’s suggestion of plug wires is a good one. If yours are original, and esp if you live in a harsh climate, that could well be the problem. Have you inspected them? Look carefully. Bend them in several places. Do you see any signs of the insulation cracking or fraying?
This could still be caused by spark plugs; among an assortment of other possibilities. Generally speaking, you cannot eyeball a plug on a modern fuel injected vehicle and determine visually if it’s misfiring, good, or whatever.