Intermittent acceleration drop

One of the issues my 2004 (V6) Tundra had for the last 6 months or so is that I would sometimes experience a loss of engine power while driving. I'd be going along the highway with the gas pedal held down to keep me at a steady 70-75, and it would just seem to lose power and slow down. I'd have to take my foot off the accelerator and then floor it, and after a couple of seconds it would catch, downshift, and accelerate back up to highway speeds.

It's been very hard to replicate for a mechanic, as it usually happened only on longer drives (1.5+ hrs), and only intermittently. Sometimes it wouldn't happen at all.

The local mechanic spent quite a while trying to diagnose it and didn't charge me much because they couldn't find anything. I do not have a full list of what was checked but:

The throttle body (air intake flaps) was clean and not sticking
The air filter isn't bad
No error codes
The rotating round piece that the accelerator cable pulls on is clean and not sticking
Fuel additives have been run through the engine several times to make sure there's no water in the gas tank
We did not change the Throttle Position Sensor, as it apparently is only sold as part of a much larger assembly ($400+?) and they couldn't find anything wrong with the existing one.

In my internet research to try to diagnose the problem, I ran across a few other people who had reported the same type of issue, but there was not any record of a shared solution.

It almost felt like it was a physical issue like the accelerator cable sticking, but for the fact that it seems to move fine. I've wondered if there's some part that's deforming just enough when hot to be a problem, maybe a bushing or something.... but if so, I haven't found it!

I'm selling this truck since I've upgraded anyway, but if there's something I can do to fix the problem before passing it along to someone else, I'd like to try.

Any thoughts?

 

I notice it most often when the A/C is in. When the compressor kicks in, I get a drop in power.

This also happens (IIRC) if you have the defog mode set, either with or without the temp dial being set to the coldest setting plus that last little click-over.

I usually drive with A/C off but was noticing similar yesterday and realized that, with these stupid new round knobs, it's harder to recognize when you're at that last-click setting. And I was, so I tapped it off, and I don't recall feeling the lag again.

I had to do a ton of interstate driving yesterday, otherwise I wouldn't have noticed.

 

Must be fucking nice not living down here lol

 

I never drive with the AC off. Even in the winter I use it regularly. Not for the cooling, but for the drying effect

 

I did it when I lived south also. I dunno.

 

How is your driveline? U-joints, center support bearing, rear diff fluid?

I was experiencing what felt like reduced power and surging at steady part throttle under load. Found my center support bearing seized and the rubber was spinning in the housing.

 

I know I've had the diff fluid changed at some point.
It's only intermittent, and not related to the AC.

 

Can't take credit for this one: But I can tell you it is a solid mod for our whips.

 

You sure?

I hate to question, but unless I’m confusing my Tundra with one of my other dozens of prior vehicles, all you need is for the control to be set to full or partial defog mode and the A/C kicks on, regardless whether the AC button is actually ON. It disregards the state of the AC button when defog modes are selected. It may also be that having it at max cool, i.e. all the way cold and that last bump beyond, and it kicks on. Or maybe I’m forgetting and you need to have a full or partial defrost mode selected.

The defrost thing bit me in the ass once. Then I realized I made one of those mistakes, I had the control set to feet and windshield defog combo mode. But I have it stuck in my head there’s another “gotcha” with control modes where you can have AC kick on without AC button depression.

 

Yes!! I just experienced this.

Same scenario. Driving along at 70 mph, holding throttle constant. Boom, slowing down. Didn’t really feel like a loss of power- just felt like the truck wasn’t responding to throttle inputs as fast. It didn’t last long enough for me to switch my scangauge to show throttle position.

It’s happened a handful of times before, and every time I’ve just told myself that I was losing my mind. It definitely happed though. For sure. No idea why though.

 

It was 100% climate control settings for me. I didn’t get it ‘til someone pointed out a setting I was using.

 

That would be the first thing that I'd suspect as well- but my A/C compressor is not functional. I pulled most of the pressure out of the A/C system to prevent the compressor from turning on, as it knocks badly.

 

Fiatrunner, I knew without looking that you must be somewhere in the north.

I had the A/C blower fan replaced a couple of years ago after the old one died. The new one has been making some noise. Could a blower/fan motor issue cause enough issues to drop power?

I'm still not sure how a climate control setting causes the engine to stop delivering so much power to the transmission. The throttle is a physical cable, so electrical draw shouldn't do it?

 

It’s typical to see an RPM drop when the compressor kicks in, unless I’m nuts? It’s putting more load directly on the engine when the clutch engages and grabs the serp belt vs. freewheeling. When my A/C compressor kicks in, it typically drops the RPM by like 5%.

 

When engaging my compressor, the RPMs would pick up. Like, it would go from idling at 600 in neutral to 800 the instant you pressed the A/C button. My truck would creep forward faster when the A/C was on. It seemed like it was tuned/programmed to up my idle speed when the compressor was on.

The loss of power I've experienced definitely isn't A/C compressor related. For sure.

It's not a small amount of loss, it almost feels like a carburetor that needs a float adjustment or a stronger fuel pump. Like you're driving along at a constant rate- and then it falls on it's face. Like you're running the carb's bowl dry. Once you let off for a few seconds and let it fill back up, it's fine. That's the best way I can think to describe it.

It's just weird that it isn't running weirdly or down on power, it just requires more accelerator pedal input to get the same engine throttle input.

 

Dunno what to tell you, your situation is different than mine, you don’t have working AC. I know with my truck I can feel when the AC kicks in, the engine bogs and the air gets cooler. Not sure what else that could be but I’m open to suggestions.

 

This sounds like what I've experienced as well.

 

Looking back at potential causes:
-Throttle body: Clean, checked it out when doing the Sea Foam runthrough
-Fuel filter: Changed in 2022 or 2023. Unmarked black filter. Are there some bad filters floating around? The timing would potentially sync up with my problems.
-Fuel pump: Until I find my notebook, not sure if this was ever changed. Apparently you have to drop the gas tank to change it, so probably not.
-MAF: Pretty sure this was checked
-Accelerator Pedal Position Sensor/Throttle Position sensor: The 04 appears to be controlled by a cable, not Drive BY Wire, but apparently there is an accelerator pedal position sensor. It's $200 on Rock Auto. How would I test this? Maybe it has a dead spot or something, but only intermittently or when hot? I do not have an oscilloscope.

From

Maybe I need to replace the TPS?

 

2005-2006 have no fuel filter.

 

V6 may be different?
But I assume your right

 

Hmmm ... I'm skeptical, but I suppose anything is possible. I don't remember seeing a fuel filter even in any of the VVTi V6 trucks I've looked up, and I've had to dig up numbers on fuel pumps numerous times for folks on the forum.

 

The one with the problem is an 04. I have a black cylinder in the right place for a fuel filter... it matches what I saw on a "how to change the fuel filter" video.

 

'00-'04 definitely had a fuel filter. And the OEM filter, per tests someone on YouTube did, flows a hell of a lot more (i.e. filters less particulate) than popular aftermarket and other OEM brands. I can only assume it's there to catch big crap that would be a problem, not fine particulate.

Similar is true with Toyota's OEM air and fuel filters. Apparently Toyota has no concern about longevity of their engine from semi-fine particulate, just want to filter out the big stuff, and the engine was designed to operate within those specs, where air and fuel can flow more freely without the added filtration. This is the main reason I won't use aftermarket filters on my truck. Only OEM. Those filters were designed exactly as Toyota had intended, for their exact engine platforms, and aftermarket manufacturers can't possibly do a "better" job building a filter within Toyota's intent/engineering.

Total side topic/tangent there, sorry. But yeah, definitely is a filter on the '04, I think @FrenchToasty and I were noticing the 2005 AC in your signature, but didn't scroll up to see the '04 in the 1st sentence

 

Can you send a good pic of what the throttle body looks like on your truck? I have a hunch.

The throttle bodies on the pre-VVTi V8 trucks (00-04) have this weird system where they are "drive by wire" for the first 2/3 of the accelerator pedal's travel. Even though there is a cable going to the throttle body, there is no physical connection between the pedal and the throttle valve until you reach that 2/3rds of the travel. Then it mechanically kicks in. I'm not sure why toyota did this- but I'm guessing for idle control via the throttle body, and cruise control. I wonder if the issue that we've both experienced is related to this system.

With the truck off, if you push the accelerator pedal with your hand, does it get harder to push around 2/3 of the way down? This could be indicative that it's got a similar system.

 

I appreciate the explanation. It sounds like that's worth a try. Perhaps I got an aftermarket filter that slowly got more clogged.
Where's my best shot at getting the OEM filter type? I have O'Reilly's and a local auto parts chain, or the Internet...

 

https://autoparts.toyota.com

 

Yes, it's almost entirely non-resistant or slack until about 2/3 of the way down. It reminds me of taking up slack on a trigger.

 

Hmm. It does look like both the V8 and V6 have a similar system on the throttle body.

The sudden acceleration drop happened to me 3 times today. It’s just such a weird issue- I really feel like it’s related to the drive by wire system. When it happens the engine still runs perfectly smooth and has great power once you push the pedal down, but just seems to respond to throttle inputs so slowly.

By the third time it happened I had my scangauge set to measure throttle position, load, and horsepower. When it happened, it showed that the throttle position stayed normal, but the load and horsepower both went way down.

Today was by far the most frequently it’s ever happened, I’ve probably only experienced it a few times before in the past few months. Wtf? I have no idea why it would do that.

I’ll see if it does it again tomorrow. It’s just so odd that it runs perfectly fine.

 

Is there an oil control valve on that engine? I had a 2nd Gen tacoma v6 that would sometimes act like it lost power and something had lead me to think it was that but I can't remember what now. Years ago. Sold truck without ever addressing since it was very intermittent and could not replicate on demand.

 

I did more research on this. I’m very suspicious of the Accelerator Pedal Position Sensor.

The truck did it a couple more times today. I don’t have enough evidence to just throw a new sensor at it as they’re $300+. Just don’t know how else to determine that’s what’s wrong. Open to suggestions.

Edit: just realized aftermarket ones are $60. Might buy one and see if it fixes it.