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stumbling 91 4Runner

Hi group,

I'm a new member with a 91 4Runner V6 4x4 that I've owned since 2001. It now has 170k miles. I have a problem with it and I've had no luck diagnosing it on my own. Maybe others in the group have also had this problem. I want to fix it before taking any long trips into the mountains this winter.

When cruising along at freeway speeds, sometimes the engine with stumble for an instant and then keep on running fine afterwards. It's unnerving, and it loses about 5-10 mph in the process. When I first got the truck, it would do it about 2-4 times per year. Now, it does it about every other time I drive it. It seems like an ignition problem to me, so I replaced the plugs/wires/cap/rotor without any improvement. I changed the fuel filter, which I assumed was the original, but that didn't help either.

The truck is driven only about 5k miles/year and about 6 times per week. All these short trips might be fouling the plugs, but the ones in there now are only about 2k miles old.

The only other thing that I can think of is the coil. It's expensive, so I've delayed changing that. Plus, wouldn't a bad coil be more of a problem at startup? The truck starts fine.

The stumbling happens when cruising, not at wide-open-throttle, and generally when the engine is already warm.

I drive a lot with the back window down when I have my dog along, and when I push the truck hard it smells pretty badly. I can tell since the window's open, and it could just be normal tailpipe emissions. (it passes SMOG just fine.) I haven't noticed much smoke at idle (when I can see the tailpipe).

Other issues:

  1. It's been about 80k miles since a valve adjustment. How important is this service? what's the downside of delaying it? power seems down from when I bought the truck. Could this be a cause? How long should it take for a shop to adjust the valves?
  2. Oxygen sensor. It's probably the original. Mileage is crummy (~15 mpg) but I think that's normal for this truck. Will the O2 sensor fail slowly? Or will it just die and give me a check-engine light? should I bother to change it if the light hasn't come on yet? Thanks in advance!!!

Eric

Reply to
91_4Runner_Eric
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Try a bottle of Chevron Techron fuel injection cleaner in the next 2 gas fillups (Target, Advance Auto carry it --- its the only kind that really works IMHO). Might just be water in gas and dirty injectors since you don't put many miles on it. Have you ever cleaned the throttle body? Were tune up parts OEM parts?

Reply to
Wolfgang

I own a 91 also, and use Techron when it feels a bit sluggish. Though, a full tank on a 4x4 4Runner is about 16 gals not counting the reserve. I recommend you fill up about 10 gal ($20 in Calif) and drive as close to empty as possible. The more concentrated the cleaner the better. The other solution is to fill up with Chevron gas, which has Techron already mixed in, but in lower quantities. Also Costco and Sam's sell a twin pack for about $8.

If that does not do the trick, you might have a bad injector.

Reply to
Joseph Wind

Reply to
Dnorthway

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