Bucking at low speed after warm-up

I have a 2000 4Runner with 427,000 + miles original engine and trans. It bucks in 2nd & 3rd gear. Not as bad at higher speeds, but can tell during deceleration/acceleration. Engine light sometimes, but doesn't last long. Any ideas?

dkm

 

Scan for codes

 

Thanks. I will scan once the light comes on again.

 

Codes should be stored. Take it to AutoZone and have them pull codes if you don't have a scan tool.

 

only bucks during acceleration/deceleration?

 

Start by changing the plugs

Plug it into a good scan tool. That will find the codes and you will solve the problem without "throwing more parts" at it.

 

Welcome and congrats on surpassing the 400k milestone. Hoping to do the same in the next couple years. I second plugs, but do the three coils and three plug wires if it hasn’t been done. OEM will run a few hundred but worth it. I also change two quarts of trans fluid when I do an oil change...

 

I disagree on the coils. They run fine forever. You can also diagnose them fairly easily.

Plugs and wires. And TOYOTA only plugs and wires.

 

Transmission flush with good oem style fluid

 

Check the colors of rad and tranny fluids. Have you changed your radiator at any point? Pink milkshake is a known issue if the two mix.

 

I had the same condition 6 months ago in my 2001 3.4 2wd. For me the problem was my Cat converter. If you want to check for this condition buy or rent a VAC gauge (they are pretty cheap or rent at Auto Zone or Orelleys) plug it into Manifold vac. Start the 4runner let come to a idle if it reads low VAC them most likely your CAT has gone bad. I chased this condition for about 2 months. To confirm the condtion you can remove the front 02 sensor and drive it a short distance and see if the condition goes away. This means exhaust is plugged some where most likely the CAT. A muffler shop can inspect for I think 25 dollars or so. If this is not it well you have eliminated one thing good luck.