Revs up then almost stalls

2000 tundra 4.7 283k miles...Just like the title truck has this issue when its warm not on cold starts, has all the usual maintenance and is in immaculate shape for being a New England pickup. I'm seeming to think its something todo with the fuel pump or something along that assembly( fuel pressure regulator, injectors, filter) along with this issue my fuel gauge likes to jump up and down while I drive. Was going to start tearing into it but was curious if someone had the issue before.

 

Several people have had similar issues before.

I think fuel pump is a logical culprit for this. I can tell you with 100% certainty it is not the fuel filter. But it could be any number of things in the fuel circuit.

How familiar with the fuel system are you? And is it a specific RPM range it stumbles? When is the last time you checked plugs and coil packs? What maintenance has been done over the years, where are you buying your parts, and what brand of parts do you normally get?

 

I’ve got decent mechanical knowledge, have been studying the tundra fuel system and hence what has led me to likely just the fuel pump as it is the original... but I almost believe it may be the fuel pressure regulator as I know that leads to hard starts.

I am the second owner of the truck (my grandfather being the first) since new. Since my ownership I only put OEM parts through it and recently just did plugs and coils as I shorted a coil during the cold days last week, And I had yet todo coils yet. as far as what my grandfather did I am unsure but given the condition I received the truck in and he was self sufficient I’m sure he did similar maintenance.

The truck only has this issue on startup and that would be warm start ups to be specific. It’ll crank over start up high idle then it will drop like it wants to die out completely so I can nurse it with a little gas and it runs just fine never anymore issues. Maybe I’ll take a video tomorrow at some point and upload it here.

 

If it runs fine otherwise, I wouldn’t go fuel pump as my number one fix. Start with MAF and throttle body cleaning. Then check vacuum lines. All of this is relatively free, minus some MAF and TB cleaner. Unhook the battery for 30 mins while you’re cleaning and letting the parts dry. Then hook back up and test again. May take a few start stop cycles or 5-10 minutes of running for the truck to settle in.

 

Also a thought that ran through my head, something I have planned for once the weather warms up a little.. have no garage and northern New England takes no pity. But definitely sounds like something that could be of fault. But what could be at fault with the bouncing gas gauge..

 

Where'd you get the OEM parts from?

 

Idle air control valve might be something else to check out as well if all else fails.

 

If it’s OEM specific like coils I just go through the dealership for parts, everything else from rock auto or Napa.

 

This and a vacuum leak were the first things that came to mind. Haven’t had this issue with the Tundra but did have it on another vehicle with brittle old vacuum lines that were prone to cracking.

 

considering the conditions where I live I would be floored if I don’t have cracks in some of the vacuum lines probably time todo some leak tests. Will have to let you all know once I dig into this and figure it out. Will get around to posting a video of the weak start ups if I remember to for others benefit.

 

Hopefully it's an obvious crack or something, otherwise I guess your engine bay has a date with a nice cigar or some carb cleaner. (If you haven't seen the latter method, search youtube for carb cleaner vacuum leak detection!)

Though it is interesting you're not throwing any codes....no check engine light, right?

 

Some googling says only the 5VZ-FE V6 uses an IAC valve; the 4.7 does it via the throttle position sensor. Maybe need to clean throttle body?

 

Yeah I’m sure I’ll be finding lots of cracks but if not I’ll just take a bath in carb cleaner.

no codes runs mint just has its startup issues checked the weather and the next few days are warm enough so I’ll see if I can’t get to the bottom of it.

 

Yeah you’d think I’d throw a code so maybe it’s faulty who knows. Or just needs a clean well find out soon.

 

Ah good. As long as you're not ordering from scamazon you should be good then. Could probably save a few bucks ordering from Toyota parts websites too though.

 

Interesting. Have you tried bypassing the fuel resistor? Or testing the fuel resistor?

 

I have not tried this but just read into it and will test it tomorrow.

 

Here is the video as promised, Hopefully the link works. But prior to the video I cold started the truck no issues like usual let it idle for a few minutes then turned it off and that's where the video starts. following the video I just give it a little gas and hold the idle for 10 seconds and it drives like normal. no codes thrown either.

https://drive.google.com/file/d/1fnKk740iyFU0zepSB0Vmnr3GcLV_cGqn/view?usp=share_link

 

My general thought process is this:

Your fuel pump relay is responsible for switching between two power feeds to the pump. One leg attached to the relay is a direct circuit, full power, when the ECU senses the pump needs to run at higher speed. The other leg attached to the relay is also power feed, but passes through that resistor before reaching the pump, which drops the voltage at the pump, causing the pump to run at a lower speed. If the resister is shitting on itself, or going bad, maybe it's causing the pump not to provide enough fuel in low speed mode? I'd check before blaming the pump.

Certain electronics operate differently under heat, some (like resistors) expected to change operation under heat, and many will start to show failure when hot vs. cold. So ... this being (1) a condition where it happens after some heatsoak and (2) it's an issue with [potentially] inadequate fuel delivery ... hopefully you get where I'm going with my train of thought....

 

Oh - and if you're in an aread with rodents, you really need to check your wiring on top of the fuel tank, with a mirror or whatever. Look for signs of rodent activity. That spot is one of 3 places they loooove building nests at and chewing thru wires.

 

After reading over a forum on it I see exactly what your thinking and id have to agree, given the way my truck preforms The resistor definitely plays a role in my issue. the middle ground of my throttle between low throttle and the floor feels like limp mode which I have just always assumed was the fact that it was a 250k+ mile v8. but that seems to be a more likely culprit. we will see tomorrow once I test it if that's the case

Yeah I Live on a farm So I would be floored if some rats weren't hanging out up there.. but I do get it oil undercoated every year and have yet to see any signs while under it. but ill give it a check this weekend, my buddies got an m12 inspection tool so that'll be real handy.

 

Because it's on the top of the tank, it's not something you've potentially visibly see. There are pics of what a nest looks like on top, I'll try to find. Meanwhile, here's a copy/paste of something from another thread:


.... these trucks use soy-based cable sleeves and hoses all over the place. This is a long and arduous journey to pursue, literal game of detective + 'cat & mouse'

They like to get up under the manifold and nest up like this.

They like to chew gas lines like this.

They like to nest up on top of the gas tank and chew thru wires like this.

They like to chew thru gas tank plastic tubes and stuff like this.

They'll chew through the gas filler neck also, which will throw codes, like this.

They like to shred air filters, causing crap to get sucked into the intake like this.

They like to systematically remove filters and replace them like this. (this one always makes me lmao)

Some guys have popped off the blower motor behind/under the glove box and found evidence of them there, or in the vent tubing, or in the evap coil housin

 

Here you go: Here's how obscured it can be, and an example of mice chewing through fuel pump wires, way up on top of the tank, hidden from view like this.

They like to chew thru gas tank plastic tubes and stuff like this.

They'll chew through the gas filler neck also, which will throw codes, like this.

EDIT: Rodents suck! One guy had them chew through the air ducts, through the wall of the duct in the cab, behind the glovebox, and chewed up all the ECU wiring. The little bastards are ruthless. But I doubt that's your issue.

 

Isn't there a thread where some guy used poison to get the mice in his cab, only to wind up dismantling nearly everything to find their smelly rotting corpses?

 

That was a 2nd gen iirc.

Anyways OP, @bmf4069 and I have replaced our vacuum lines with silicone from here.
https://www.siliconeintakes.com/silicone-boost_vacuum-hose/

I've ordered the master kit and dress up kit. Did 4 vehicles with one or the other. Can't remember

 

Really? I wonder why it's listed under part #89672-47010 "Fuel Injection Idle Air Control Valve" for the 4.7L V8. I'll need to check further.

 

I remember the one guy who found a corpse stuck in one of his valves. It was in one of the threads I linked above. My guess is it was a classic case of "mouse chews up air filter, mouse goes upstream and finds itself in a precarious sitch.

 

How funny. Yeah I was just summarizing some guy on another site (who admittedly stated it quite authoritatively so I took his word for it), basically one step above pulling it out of thin air.

I went ahead and searched the FSM for “idle air” and got the following two relevant hits.
This one is specific to the 2UZ/4.7/V8:


This section only talks about the 5VZ/3.4(?)/V6, and there isn't a comparable section for the V8:


Bill, buy that $350 part and see if it goes somewhere.

 

Damn you, now I’m gonna have to look for it tomorrow when it’s lighter out. haha

 

Hey NHboondocker - did you ever get this figured out? Follow up?