WELL after testing everything for months I pulled the new denso O2 sensor out and replaced it with a new Bosch which I might add looks a lot more heavy duty and this truck now runs like a dream. And to thing that it would occasionally run great for a few miles then fail again. Never heard of an intermittent O2 sensor!!

91 3VZE 4runner code 25
my code 25 started out with it would drive fine until almost warmed up then loose power and runs a little bit rough. I assume the change occurred when it went into closed loop. Eventually he got to the point where it runs low on power all the time. It idles fine. But here's the kicker twice in the last months when out on the highway at 55 miles an hour on a 30 mile trip. It runs good enough to drive but its low on power and suddenly the truck snorts for a millisecond like it's lost power and all of a sudden it's running like a dream. All the power is there and the check engine lights off. I go about 10 more miles and boom down goes the power check engine light comes back on. It's done this twice in about the last hundred miles of driving. I've had the truck since new. It has 120,000 miles on it. My wife got it in a divorce and parked it for 10 years and I got it back about a year ago. I had to replace the entire fuel system meaning fuel tank and lines. I've checked the fuel pressure ignition systems brand-new full tuneup. New denso oxygen sensor. I've removed and cleaned all of the ground cables on the engine. I replaced the coolant temp sensor. Check for intake and vacume leaks. New exhast no leaks When it runs good it runs like new so I have eliminated it the idea of problematic injectors. My buddy has a truck identical to mine same year and I used his air cleaner parts to double check the MAF and air volume unit. No change. But the way this thing turns on and off is a symptom I've never heard. Gas mileage is very bad so it must be very rich Anybody got a comments

 

Hmmm. A partially blocked injector would be one of my first guesses.

Code 25 is a "lean malfunction," meaning the system is trying to get the O2 in the exhaust down, but can't. If you have a clogged injector, the system can't add enough fuel to get the O2 down, the engine will run "rough" (a non-firing cylinder, most likely), and if you shake it enough the clog might move for a while "curing" the problem. (temporarily). Direct testing of injectors is no picnic, but I'd at least pull each plug to see if one looks especially "lean," and do a "cylinder efficiency test" (pull each plug wire one at a time, to see if one cylinder produces no change).

Vacuum leaks can overwhelm the ECU. You've checked for leaks, but how? "Traditionally" an unlit propane torched waved around the induction system is a pretty good test for leaks.

Low fuel pressure can cause a code 25 (none of the injectors are putting in enough fuel). The easiest way (IMO) to test this is to plumb in a 12mm banjo to Schraeder fitting at the FPR. This gauge kit has the correct fitting.

Of course, you should directly check the ECU's report. Here's how to check that the O2 sensor is "flopping" at the right rate: http://web.archive.org/web/201003261...01heatedox.pdf

 

thanks
as to the injectors I have a hard time with one working perfectly then not. Idle is very smooth. we have run 10 bottles of redline though it last summer and it did get better and better but we had no code 25 back then. The tail pipe is spotless showing to really is lean.We do know we are not loosing a hole cylindar becase we grew up in the 60's with old school hot rods. I guess we can try the pull the plug wire game but they are a pain and unless the truck is under pretty good load it runs great with no check light.Vacume and intake were checked twice with Acetylene.This intermittant thing leans me away from that too. I will try wiggleing the hoses I guess.. static fuel press check was good. I have the gauge and will look onto that but again Its an on off situation. Today I put a new bosch o2 in with no change but will do the test. The link is bad but you mean the 8 times in 10 seconds in the service manual? Right? Or the on off one opening the throttle. That on was good.

 

Any other ideas

 

I battled an intermittent code 25 for almost 2 years after rebuilding a 3VZE in a 94 pickup. I chased lead after lead but refused to believe it could be an injector problem because I installed a nice set of re-manufactured OEM injectors from Rock Auto. When the problem got progressively worse - I finally checked the injectors and found the problem

 

Thanks dan. I was hoping not to go there but if the fuel pressure check ok under a load I will give up. I would really hate it if I did the injectors and still had the lean burn. I still find it hard to believe that after running lean for 1/2 hour it can suddenly take off and run perfect with lots of power for 5 minutes and then suddenly go back to lean...I hate the gizmos on these 3.0's Wish I would have kept my 1980