Laura here again with the almost-300,000-mile 22-E engine in a '93 truck. She's been running rough-- hesitating, backfiring, bucking a little bit-- for a couple of months now. The weird thing is, it'll sometimes be 30 miles between such episodes. She'll run like a charm, and then i feel that sense that beats are being missed. Sounds and feels choppy. When i stop to get the gate, i can hear a soft backfiring from the exhaust. She's such a GOOD LIL TRUCK that she hasn't actually stalled out, and she always starts strong. Just has this occasional (about half the time) and unnerving bad behavior.
So i ruled out loose gas cap (loss of compression), and don't think it's water in the gas. Took her in and got an oil change, check on timing, fuel filter, tightened belts-- all those things are good. The mechanic replaced the spark plugs, showed me the old corroded ones, and said, "I'm sure that was your problem." But a block down the road, and she was at it again. Bucking and jerking all the way home. (I looked up a few other things that don't sound like the problem: O2 sensor, probably not-- no weird smells or black exhaust. Coil, probably not-- no trouble starting. Spark plug wires-- apparently were not replaced with the plugs themselves-- could maybe be that?)
I am told this might be the distributor cap. Before i go back in and ask for a new one, i wanted to ask you experienced Yota Lovers: Can this be an off-and-on problem? Or would it always be constant, once it began?
Any other suggestions welcome. Thank you!

 

Wow 300k miles, that`s great. You didn`t say when the last time distributor cap, rotor, plug wires had been changed last. If these are original then absolutely I`d change them. I don`t know that changing those things will cure your problem, but again depending on how old they are they quite possibly need to be changed. Also, there is an o-ring under the distributor cap that gets dry and brittle, I would change that as well to keep moisture out of there. These items, the plugs, wires, dist cap, rotor and the o ring I would order from Toyota and bring them to your mechanic the OEM ones are just so much better than the parts store ones. You mentioned fuel filter, so I assume that means it got changed. But again depending on the last time certain items have been changed, I would also look at the air filter. Adjusting your valves is also a good idea. Again all of this is just regular maint interval type of stuff. There is also an oring under the idle adjustment screw that dries up and gets hard, that can eventually lead to a vacuum leak. I would change that o ring as well if it has never been done to your knowledge. With all of that done, I`d have him adjust the idle because now the screw got removed and put back and see how it runs.

One thing to consider if the stumbling does not get better, perhaps after 300k your injectors need to be serviced. If they have not been serviced ever, then boy I would certainly think about doing it.

 

Hi and Thank you so much! I am thinking to bite the bullet and just go to the Toyota dealership to get the work done. They're more expensive, but stand behind their work, would automatically use the quality parts, and maybe at this point i need to be REALLY good to my truck!
So-- Distributor cap, wires, rotor, and O-ring underneath that; and possibly the O-ring under the idle adjustment screw, which should also be adjusted.
If that's not it, we'll get into injectors, valves, etc. I can check the records (i have a big stack in chronological order) to see if it's had the injectors checked and when the valves were last done.
And yes, fuel filter and air filter are good. (I check air filter often, as mice have gotten in there and nested before. Easy to check, old ladies can do it, lol! Discovered one of Toyota's few design flaws... a little rodent highway with no screen, about 1.5" diameter, directly to the air filter box... i did try to jam some hardware cloth in front of it but think a very determined small rodent could still push his way around it.)
Still wondering if the fact that the trouble is not consistent but sometimes non-existent is any kind of bright clue!
Thanks again, i really appreciate the educated advice!