3.4 Taco Bucking/surging under acceleration (FIXED!!)

So I have a 2002 Taco with the 3.4 and manual tranny. Last week it suddenly started bucking/surging under moderate to full throttle. Feels like it hits a wall and won’t get over 3k in gear, but will rev freely with the clutch in. Light throttle it runs smooth, but doggy. I’ve noticed in the past couple of years that I’ve owned it that it would run great one day, and kind of doggy the next, but it never had this issue with the bucking before. Just changed the coils, plugs, and wires for Denso OEM stuff today. Idles and drives way smoother, but the issue is still there. Anyone else have this issue? Truck has around 290k on it. Thanks!

 

Update- Replaced fuel filter, and condition improved quite a bit. Old filter was pretty crusty and hard to blow through, so it had to be somewhat restricting flow. Going to drive the truck the rest of the week and see if it improves. Fingers crossed lol. Still has like a 200 rpm window where it surges back and forth, but now I can get past it if I stay in the throttle.

 

Chased down the "bucking around a specific RPM" issue for a long time on my '00 and it turned out to be the TPS.

https://www.tacomaworld.com/threads/misfire-mystery.820093/#post-29419357

 

My truck is a 2002. Am I able to buy just the sensor, or do I have to get the whole throttle body? Seems there was an APPS sensor tied to the TPS at some point. Mine has the cable throttle. Not drive by wire. Thanks!

 

So my sensor was a 3 wire, and is able to be replaced by itself. Replaced it w a factory Denso. No change. Cleaned the MAF as well. No change. Surging is only present at approximately 50% throttle. Light or full throttle it is not, but truck feels like it’s fighting against itself the whole time. Slightly doggy overall, but since the fuel filter swap, I have more low rpm grunt than before. It’ll pull hills at low rpm’s in 4th and 5th where before it didn’t want to. Anyone know what my timing and fuel trims should be at normally? Just got a new scan tool that reads that, so it may be helpful. Thanks!

 

Check your clutch. My 95 started this new bucking like it was maybe the tranny slipping. I’m still diagnosing this issue now. But mine only started bucking after I replaced my master cylinder then on to the slave cylinder and she still bucks me. Lol

 

Clutch is good. Drove the shit out of the truck yesterday trying random stuff to see if I could get the condition to change. Pulled the vacuum off the fpr to see if maybe I could get it to run a bit rich to see if it was a fueling issue. No change. Seems like the surging is only present at 40-70 percent throttle. Below that and above that it doesn’t do it, but even when it’s not doing it, it seems like something is holding the truck back. Front A/R sensor is going a good bit above and below 3.3v when driving, and the rear sensor shows no volts at any time. No CEL for anything other than an emissions related one that I believe is probably a vacuum line in the charcoal canister system under the bed. Looking at the data as I drive, nothing jumps out when it’s surging. No cels ever or pending for misfire, lean, ect. I just replaced the plugs, wires and coils with Denso OEM stuff, and the plugs looked lean. (Light colored). Manifolds also look like they’ve been getting hot just by the color. I’m starting to wonder if the cats may be partially plugged. The truck has almost 300k, so that’s definitely a possibility.

 

Checked the heat with a laser thermometer after driving the truck hard on the way home. This was immediately after I shut it off. The manifolds seemed to have one cylinder in each side which was hotter than the rest. The driver side center cylinder was 330 while the other two were around 280. The passenger side rear most cylinder was 380, and the other two were around 280. Before the cat was 280ish and after was 100 degrees higher on both cats. I’m assuming there are two, as both are between the a/r and rear O2 sensor. I thought one might be a resonator, but that position wouldn’t make any sense. Inwas hoping to see some high temps before the cats to indicate a blockage, but not so. They should be about 100 degrees higher after the cats if they’re working right. I’m gonna test it again tomorrow with the engine running at about 2500 to see if there’s a difference. Just out of curiosity today I filled up with 93 to see if maybe that would make a difference if for some reason I was having pre detonation and the engine was pulling timing. No change. I ran the piss out of the truck on the way home to see if I could get it to throw a cel. No luck lol.

 

FIXED!!!!! Rear cat was almost completely clogged. Hollowed it out and the truck had easily 3X the power, and no bucking or hesitation at all. Apparently the truck has always had a clogged cat since I’ve had it over the past 2 years. Attached is a pic of the cat with a light shining through it.

 

did yours do it all the time or just most of the time... cause sometimes ill start it up and go and itll run Perfect, sometimes for even 10 mins then it starts the bucking. replaced my plugs and fuel filter and deciding where to go next