Drivability Issues

Hey everyone, I’m new to this forum. I’ve got an 01 4 runner with 180k miles on it that I’ve had for 3ish years (bought with 129k miles). For as long as I can remember now, I’ve had a super annoying issue that is beginning to get unbearable. I’ll try to describe the symptoms as best I can so bear with me.

- When you approach 3.5k RPM (flooring it), you can feel it lose a bunch of power. It pulls good right up to that point then falls on its face. Now, if you let off the throttle justttt a little bit, it’ll pick the power back up.

- When on the highway getting up to 70ish it’ll do the same thing I described before. You’ll hit about 70 and it’ll fall on its face. You have to really fondle the pedal until you find the sweet spot where it’ll start accelerating again. Don’t bother flooring it because it’ll drop a gear, rpm’s will go up, but the speed will not change at all.

- That same problem was super prevalent when I towed a camper. Single lane highway with a bunch of cars behind me towing a small single axle, we got to a hill and as I started to ascend the hill it just started losing all of its speed. Flooring it did nothing at all. I got stuck at 35mph in a 55 and I couldn’t get it back up to speed for a few miles.

I’ve replaced a lot on this thing but I don’t remember everything enough to make a list here. If you do mention something, I’ll let you know if I’ve replaced or taken a look at it.

I do have knock sensor codes (replaced them and they went bad again), and a bank 1 lean code. I’ve smoke tested the engine multiple times and fixed any leaks I found. I’ve also replaced the 02’s and I’ve cleaned the MAF.

 

As i was reading it, before i got to the knock sensor codes, i was literally thinking knock with the ECU pulling power.

1) our current gas is cheap water
2) your vehicle was designed and tuned for 100% gasoline
3) if you are towing a camper you REALLY need to be running 93 octane
4) if you are flooring it everywhere, you should be running 93 octane

The current gas we have, is pretty bad. Your knock sensors are picking up "ping" or "knock" which is when the cylinder fires on its own, before the spark plug fires off. This happens normally as the piston is coming up in the cylinder well before the piston is at the top of the cylinder. The knock sensors are listening for "booms" or the combustion mixture firing off before the spark plug fires. If the ECU senses "knock" also known as detonation, the ECU pulls a bunch of timing to save itself. This is trying to keep you from knocking the rod bearings out and having a rattling mess of an engine. You should up your octane first, but then i would also start looking for other things like your spark plugs. Pull them out one at a time and carefully inspect them. See if one spark plug looks different than the others, which would typically indicate that one cylinder is getting more or less fuel than the others. This could lead you towards a bad injector and a cylinder thats lean which will generate higher cylinder temps and increase the likliehood of detonation in that cylinder.

 

I’ll take a look at the plugs. I have replaced them and the wires. Plugs used I believe were Denso with the dual probe things coming off of it (sorry can’t remember what it’s called lol). And I’ll see if one looks fouled or anything. I did replace the knock sensors with dirt cheap rock auto ones which is what I was thinking is the problem for that code.

 

I'd avoid non OE replacement parts when possible. Diagnosing will become harder and harder if you throw a bunch of junk sensors into the mix.

Other than that I would probably read the plugs, check for spark. Clean the throttle body. If the problem persists I'd check for vacuum leaks and then do a leakdown test on the engine just to verify engine health. After that Id start looking at fuel pressure and possibly test/ replace injectors.

IMO It sounds like your rig is pulling ignition timing... Just need to figure out why. Knock sensor, MAF, or 02 sensor is a likely cause once you verify you do not have vacuum leaks, spark, or detonation potentially caused by fueling issues...
But I hate to start throwing money at sensors without knowing for sure.

 

This^. Hopefully you kept your original sensors?

 

Fixed all vacuum leaks when I did a smoke test about a month ago. Not much of a change at all. I last changed the plugs/wires at 160k miles so they're 20k miles old. I did not use OEM sensors on much of anything as I couldn't afford it. Unfortunately, I can't remember if the 02's were ever replaced. The Cats were replaced maybe a year ago with ebay rip off's.

 

Uhhhh no. When I replaced most of these sensors, I didn't quite realize for some reason toyota's suck with aftermarket parts, unlike my mustang haha. However, the knock sensors were literally falling apart in my hands so wasn't much use keeping them anyways.

 

I do feel like I should include this. I CANNOT remember 100% if this problem existsed before this, but back in 2022 I took a beach trip and my fan clutch went out while in 4lo. Didn't see the temp gauge, and I overheated it. With no coolant to be found, I drove it back off the beach after cooling down and actually made it a very long ways (long enough to get to a safe place to wait on my dad to tow us home), but by then it had shut off multiple times and sounded like a tractor. It actually blew the top of the radiator apart. Before this I don't believe I ever had any CEL codes. That is when my knock sensors went bad. After returning home, a new rad, coolant, and fan clutch were installed, and I haven't had any issues. Never any symptoms of a headgasket leak or cracked cylinder.

In terms of other symptoms, I forgot to mention it does have a surging idle. It'll surge from 600ish to 800, and you can actually feel it surging as you accelerate through the RPMS. Doesn't matter if you're flooring it or taking it easy.

 

I put in 93 a couple days ago. Been through half a tank. I do feel like there is a little more power for sure, but all of the symptoms still exist unchanged

 

Did you pull the plugs out and see if one looks different from the others? Maybe you have an injector that is stopped up or not spraying. If you have an injector that is spraying half of what it is supposed to spray, then that cylinder will be lean and that cylinder being lean will run MUCH hotter cylinder temps and combustion temps. This hotter cylinder and combustion temp can turn that cylinder into a diesel where the cylinder and piston are so hot, they ignite the fuel mixture as the piston is coming up in the cylinder BEFORE the spark plug fires. Hence the knock sensor picking up ping.

After reading your response above, about being on the beach and overheating and driving back with it shutting off multiple times and knocking. Ouch.....