the code still hasnt came back on yet and it seems im getting a little better gas mileage...i pray it stays off for good!!!!!!!!

 

Hope it was that pinhole. I'm still searching for a cause.

 

The guy knows what hes talking about! Those o2 gaskets turn brittle after a while, so I would start there. from there, closely inspect the rest of the system(up to the o2 sensor) and look for leaks. the slightest amount of fresh air getting in before the sensor will throw the readings off, and a code 25.

Vacuum leaks.... another cause of code 25. they can be extremely difficult to find, so pay extra close attention while sniffing them out. Just remember... there are 10,800,420 miles of vacuum lines in these rigs (maybe a lil dramatic ) and all it takes is a slight leak.

 

I have the same problem on my 95 4runner. Didnt pass smog with twice as high readings for HC and CO. Then code 25 came up. After i did the heads when i got it , i replaced:

Cap and rotor
spark plugs and cables
air filter and air box (K&N filter charger)
02 Sensor
All gaskets from heads above
Replaced the VAF

Ive heard that the 3-VZE only likes the OEM Denso 02 sensors, so im going to return this and try it.

 

Finally found mine. It was a 2 part combination. I purchased a new denso 02 sensor. Also the metal "rats nest" of vacum tubes that are found between the head and the throttle body ha d a vacum leak from one of the tubes having been bent from when my Brother in law rebuilt the engine. I call "bull" on the the exhaust leak theory unless it is with the actuall o2 sensor gasket. My LCE header has a wicked leak and my code 25 is gone. My truck ran great with the code 25. I got 20 MPG, never stuttered, and had plenty of power. That's what puzzled me so I just saved up and got a new o2.


My brother in law couldn't find the problem so he took his CEL light out of the dash then later after I purchased it he told me it was missing. So he had been running with it for a long time with no problems. my old o2 was shot.

 

Somehow I missed this one when I first started my thread about the same issue. Truck runs great, shows code 25. My gas mileage is poor as well, getting 14 mpg highway with a new straight-through exhaust system (should be more than that, it was at 15.5 when I first got it to years ago and it was stock!). Code came up the day I got it from the muffler shop. I will check what you guys recommend, hoses, o2 gasket (o2 is fairly new, 7 months old ~3000 miles) and a visual and audio check of the exhaust. Hopefully that will do the trick!

 

My truck throws a code 25 as well. I believe I have a burnt exhaust valve on cylinder number 6. The unburnt air is what is causing the code (I think), cylinder has ~50 psi. I've heard valves burn on these motors from not adjusting them. Are you sure you're getting complete combustion in all cylinders? My rig idles a bit rough but I still get almost 20 mpg on the highway. For years I never knew I was running on 5 1/2 cylinders!

 

I had the same problem (like many others) with my '95 4runner, when it was running lean, (25), i had replaced my 02 Sensor, when i swapped it, it was still running the same code, so i made sure i ran with the "DENSO", seems to me like the 3vzeey only like OG parts. By the way, I am a Californian with only '1' 02 sensor on my truck, so it helps not having both.