Slight buck/power loss

I’ve got a 2002 xtra cab 4x4 3.4L with 160K. Trucks been hesitating recently, seems to be getting worse. Seems to run ok for first ten-15 minutes then acts up. I occasionally get a P0420 code and the evaporative emission code, (I think it’s P0440, no CEL currently to doublecheck that) I usually get them simultaneously. Over the last 4 days I’ve been experiencing a slight buck or hesitation, like the engine is losing fuel for a split second or something. Started out seemingly only at highway speed but today was doing it around town. In the last two days I’ve replaced all 3 ignition coils, plug wires, the air filter and TPS. I’ve also cleaned the MAF. Timing belt and Plugs replaced with new split point 20K ago. I’m leaning towards replacing the fuel pump, but I wanted to get some opinions on the cat code, or any other thoughts on the cause. Any pointers would be appreciated -thank you

edit to add that downstream 02 sensor, evap purge valve, fuel filter were all replaced 20K ago, and also throttle body removed and cleaned

 

Possible carbon cannister. Any smell of gas near the bed?

 

Yes, occasionally. Would that cause the hesitation? It’s been throwing that evap code for two years, and I’ve seen other people with it in non-emission states that just clear the code and keep going. So that’s been my approach.

 

Another one of my vehicles (not a Tacoma) had an issue where the idle would dip down too low as I was coming to a stop, and it was difficult to get a clean take off with the clutch without it bucking a bit. Once I fixed the EVAP issue I had been ignoring for years, all of it went away.

 

Ended up being a wire that I'm assuming a critter chewed through. Sometimes its not too bad.

 

An update: I just took off the throttle body and thoroughly cleaned it and the gasket. Reinstalled and replaced both TPS and MAF with brand new. Took it for a run on the highway and still bucking under acceleration. Seems to need ten minutes of driving before it will start doing it. Also, if I put it in park and rev it up to 2500 rpm it doesn’t do it. Seems to only happen when moving. Doesn’t feel like a transmission issue but I’m not experienced enough to be certain of that. I guess next step is replacing fuel pump. I’m just throwing money at this at this point.

 

Yet another update: I just got a P0171 code. Never had this code the entire time I’ve owned it. Just appeared after replacing MAF with $150 Delphi part (it was best they had and unreturnable so I hope I didn’t make a bad decision) anyway a quick search led me to a thread with someone with the same code, ended up being fuel pump. I just got back from the store with a new Denso pump and I’m about to attempt this. The other poster has a 2010 Tacoma and mine is an 02, so is it likely my problem is the same as his? Fingers crossed

 

Good luck and hope the pump solves it. If not, I just helped a friend get his '98 Tacoma running right by swapping in new injectors. Actually they were some used injectors I had lying around, but nonetheless that solved his issue.

His truck would buck/hesitate to rev between 2-3k rpm consistently, but otherwise ran fine both below and above that rev range. Before the injectors we tried MAF, TPS, IAC, throttle body cleaning, new plugs, and nothing worked until we did the injectors.

Not quite exactly the same thing as yours, but don't rule your injectors out just yet. FWIW his truck has ~400k miles and the original injectors made it that long lol.

 

Well got the fuel pump replaced. Wasn’t that bad really. While the bed was off I shed a tear for the rust I had to chip away from the fuel tank crossmember. That thing is going to need replacement. Anyway, fuel pump didn’t solve the problem. Next thought is plugged cats. So I ordered all new exhaust and cats, they be here in pieces over next two days.

 

Keep us posted, sorry to hear it’s taking so much effort.

 

From this list, appears you addressed many of causes
IMO
injectors or cracked exhaust manifold would be next on my list

 

I ordered all new exhaust from the exhaust manifold back. It was shipped in 4 packages. 3 have arrived, one seems to be hung up 2 hours away for some reason according to tracking. As soon as it arrives im ready to bolt it all up. I saw in another thread where it was recommended to run a tank of top tier fuel if you think your cats might be bad. So I’ve filled up twice and it doesn’t seem to be hesitating as bad. I’ll update after the cats are on and if that solves my issue. I’m grateful to you all for the tips and replies, thank you.

 

Did you replace the IAC or just clean it? I had a similar problem and a new IAC fixed it.

 

No i just cleaned it. Did you get any sort of code from it?

edit to ask: i just replaced both cats and it’s still doing it. Doesn’t do it until it’s really warmed up, like 15 minutes of highway driving. Then starts bucking. The harder I press the accelerator the worse it is. I can feather the accelerator to get around. I’ve thrown $1200 at this so far and still don’t have it solved. I’m pulling my hair out.

 

Have you considered new/reman fuel injectors yet?

 

No, I haven’t. I will do some research on that. See if it’s within my skill set. Thank you.

 

Question- is it possible for an injector to be bad and only show problems while in motion after fully warmed up? If I sit in the driveway and hold down accelerator it doesn’t do it.

 

In my experience yes, even though it doesn't seem that'd be the case.

Recently helped a friend swap injectors. Prior to doing so his truck would buck under acceleration between 2-3k rpm. Outside of that rev range or idling in place it ran perfectly fine. Injectors fixed it

 

Well my next step is gonna be test the injectors. Won’t cost me anything but time. If I find a bad one, I’ll replace them and see what happens. If they’re good, I think it’s time to throw in the towel and call in a pro. Would a bad injector cause a check engine light?

 

Doubtful, but the effects of a bad injector might, misfire etc...

Look to Motorwest for injectors. If you've got a v6, you want the "Denso Upgrade" kit. The job itself is pretty simple. Only special tools you'd need are crows foot wrenches for the fuel rails, but they are a great tool to have. Highly suggest using a very light application of super lube on the orings as opposed to gas like the FSM suggests. Check out the Timmy video for the whole job.