Chooch

Trucks running rough from idle to about 3000rpms its rough then smooths out. Sometimes it completely goes away but always comes back and is rough again. Threw a code 25, which means its running lean. Now it started running rough after I tried cleaning out the throttle body with some carb cleaner. Pretty damn sure the stuff I used was not sensor safe. Im thinking I screwed the o2 sensor, unplugged the sensor and went for a drive, drove exactly the same not any worse or better. Any other way to test the sensor? Or do you think my sensor is done?

scrosst4r

I had same problem with same code. Pulled TB off and injector under the TB had a jacked up clip so it was barely connected and would miss/throw CEL intermittently fixed the clip n shes running good now. Slim chance its same problem but worth a check.

Gamefreakgc

I'm chasing the same code. I cleaned my TB with carb cleaner as well, didn't think about if it could ruin it...

scrosst4r, what does the "clip" look like? Are you talking about a hose clamp or is this a wiring connection?

scrosst4r

On mine it was the actual electronic connection to the injector .

Chooch

Got an new Denso O2 coming from Rockauto anyways. Ill check that injector though

scope103

There are lots of causes of running lean, but an air (vacuum) leak in the intake is the most obvious one. The leak allows "more" air into the intake than the VAF sees, so "not enough" fuel is added. Based on feedback from the O2 sensor the fuel trim shifts up, but it eventually hits the limit and throws the code.

I've never tried it, but I'm told an unlit propane torch will help you find a leak. But you may have a fairly big one (like right at the intake to the throttle body) that may be visible.

Gamefreakgc

I forgot to post this earlier. I've been chasing the code 25 on and off for three months. Here's my thread on what I've tried so far and the advice from others: https://www.yotatech.com/forums/f116...-3vz-e-258926/

I got a lot of good advice from others, it's worth checking it out. There's a lot of issues that could be going that you're not aware of. At this point, I checked the resistance on the o2 sensor and it's waaaay outside of the FSM specs. I'm wondering if the shop I went to put the right one on. Pretty sure that's my problem. I'm going to run some seafoam and water injection first to clean the engine out before I switch out the o2 sensor, since it could ruin my new one.

sactoyota

In most cases it is not the oxygen sensor at all. I had a code 25 and could not figure out what was going on. I did the tests above and couldn't get a reading other than lean, even though the truck ran great. The problem with trying to figure out code 25 is that it takes a couple days for the check engine light to come on again as the computer adjusts more to compensate until it is out of range. The only way I was able to figure mine out was by installing a air/fuel ratio meter onto the Ox diagnostic port. I changed my EGR, water temp sensor, and all injection equipment and it continued reading max lean.

Finally while messing around in the engine bay I bumped a vacuum line going to the VSV's and had a momentary rich reading on the meter. Started cliping the ends of vac lines to get fresh hose connections and all of a sudden the truck read perfect air/fuel ratios (bouncing back and forth between rich and lean). I had previously sprayed carb cleaner and starter fluid on all the hoses and had no signs of idle up indicating a leak, and there was no audible signs of an air leak. I never would have known I had found or fixed the problem unless I had the air/fuel ration meter hooked up to get instant results. I suggest that anyone with a code 25 use an air/fuel meter so you don't have to wait 4 days for the engine light to come on or stay off...

Gamefreakgc

Where would one obtain an air/fuel meter? I googled it and it came up with a bunch of gauges... not sure that's what you are talking about. I'm about to check the rest of the "code 25" system while doing a valve adjustment so I'll be messing around in the engine anyway.

Co_94_PU

iTrader: (-1)

Yep it's just another gauge, specificly it's a pulse counter I believe. They should all list, atleast the good ones, what systems they are designed to work with.


The oxygen sensor is located in a recess in the exhaust tube it's unlikely to be damaged by carb cleaner, carbon chunks maybe...

I just replied to another of these code 25 threads, here, and I'll add an addendum to it now after glancing at Gamefreakgc's thread. I realized I overlooked something.

mtech4321

Okay, Heres is my Question, I just finished putting a New motor in my 89 3VZE ex Uhaul box truck. The previous engins had all kinds of compression problems, head gasket problems etc and it finally crapped out so in goes the Brand new Reman engine, Truck runs great. Every thing has pretty much been double checked etc. I it throws a code 25 after it is started and you rev it up passed about 2500 RPM. From what I am reading above the ECU modifies it base fuel maps over the long run and assigns MIN/MAX increase decrease of Base maps, and these maps self correct as time and conditions change. If this self learn process i am understanding is correct. Than the ECU needs to learn the new engine and in short order this code will go away. Yes or No.
A few things to consider.
1. we have put less than 100 miles on the engine and no one interval was more than 20 between Key on start ups.
2. O2 sensor is new.
3.we have tripled checked all vacumm lines and have no vacum leaks.
4. there was no check engine light or codes on old engine even as crappy as it ran.

Is there a way to reset the ECU correction strategy

bone collector

pull the efi fuse and wait a minute then put it back in. that should reset the computer.... then go from there

mtech4321

Pulling the fuse reset the Code, but I dont think or no if it resets the learning stratagy.

bobcat20

Hi, I think I have found a fix for the common code 25 (engine running lean) problem. I had this issue on my otherwise fine running 3vze engine for years -completely stock motor -one day I was listening around the base of injectors with a mechanics stethascope and could hear air movement sound at the base of two different injectors but not at any others.Now this motor would run fine and would only set the code 25 after idling for a while. I decided to pull the injectors and what I found was that on those 2 injectors the o-ring around the black plastic/bakelite injector holder (the part that sits in manifold and that the injector plugs into) -both of those 2 injector holders had broken o-rings causing air leaks which caused the code 25. Now I think this is probably a frequent cause of this code 25 as these o-rings are pretty wimpy little things -about an inch in diameter but thin and could easily be disloged or even broken while pushing injector holder into place and also will degrade with time and heat. Some people have reported having the baklite/plastic holder itself being cracked although mine were ok. When installing holder with new o-ring -first clean out recess when holder plugs in -there is a sorta groove/flat area that gets carboned up, then put a little oil on ring and twist it into place -might as well change them all-youre in there-this will fix code 25 for many of you.