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'01 Toyota 4-Runner - Hesitates and Bucks

Our 4-runner has been reliable since the day we bought it. It is just now showing signs of its age; a little rust on the bumper, brakes are getting replaced for the first time this weekend, etc.

Here’s our problem: The check engine light had come on and off for the past month. Last week, I noticed that as I was coasting around 60mph, it bucked (like a couple jolts) and then went on its way. I wasn’t hard on the gas. We took it in for service Friday and the o2 sensor was the culprit of the check engine light. We figured the problem would stop. It has actually become worse. When at a stop and you go from putting your foot from brake to gas, the initial pressing of gas pedal is met with what I can only describe as a palpitation. It does not do it every time (maybe 50%?). Then, this morning as I got on the highway and was at the end of my acceleration (60mph) the “bucking” happened. Then, in traffic at 40mph, then at 50mph going up hill, then again… It goes away if you let off the gas for a second.

Any ideas?

Lots of ideas. How old are your spark plugs & wires? Air & fuel filters? If any basic maintenance such as this is even close to being due have it done. (Or report what has been done when). Many issues like this are from things exactly like that. While someone is doing the basic maintenance items it wouldn’t hurt to ask them to check the fuel pressure.

If the check engine light comes back on take it to a chain-type auto parts store. Most read the codes for free. Write down the exact code (e.g. P1234) and post it.

I think its been a while since the plugs were changed. We’re going to change them out tonight. Air and fuel filters are recent. Transmission fluid has been replaced within the last year. Will let you know if the plugs fix the problem. Thanks!

Inspect the wires carefully as well. If they’re just standard plug wires these aren’t too expensive and you should just change those too. At the very least, at some point tonight while under the hood run the car in the dark and watch for any electrical activity in the vicinity of the wires which would certainly tell you that they need to go. If the insulation and boots are all in good shape you can also check the wire resistance with an ohm meter. You’d have to search for resistance specs - probably something in the no more than 5K ohms/ft range.

The signs of trouble you are having could be due to a lack of fuel. If you haven’t replaced the fuel filter try that. If that doesn’t help then the fuel pump may be having trouble.

We changed the plugs and the problem has stopped. Thanks for your help!