Bank 1, Sensor 2 - 02 Sensor issues

[lstevens76]

Ok, so the car is running but having a few issues but let me explain first.

 

When I first got it running I knew the car had sat for a few months and I used the previous engines intake, sensors, etc....  What I replaced was the long block (a literally long block just block + heads + cam sensor is all that was present and the knock sensor was the wrong one for my car so used the one from mine) into the car.  All other components were what was on the car.

 

The long block had been sitting for 6+ months I believe so I expected some issues as stuff got cleaned out, etc... 

 

First I got a P0136, which I cleared.  Then I got a  P0420 which I cleared, then I got a lean code (don't remember the code) which cleared.  I also ended up with a knock sensor code (which I cleared).

 

Out of all of those one keeps returning with symptoms, the P0420.

 

Upon researching the symptoms I found this post over on NASIOC with exactly the same driving symptoms I am having:

 

I have an 03 baja 2.5 n/a that had a very wierd problem. When driving and you let off the gas to coast, upshift, downshift, or just to come to a stop, the engine would surge almost like tapping the brake pedal every 2 seconds. Then when at a stop, the idle would surge up and down and then finally settle. It was at the dealership for almost 2 weeks with them working on it every day, and after all was said and done it was the rear 02 sensor. It was the strangest thing either they or I had ever seen. They replaced the IAC, throttle body, tps, front 02, engine ECU, and then finally when they replaced the rear 02 it went away. There were no codes, and no indication that anything was malfunctioning when you looked at the data on the scan tool. Wierd ****. So even though yours obviously doesnt have the symptoms that mine had, it could very well be the rear 02 sensor, they can act very strange when going bad. If you replace it you should use an 02 sensor socket so you dont strip the nut on it and have to cut it out. It looked like it wasnt too hard to get at....Good luck, and post if it helped or not.

 

 

I've already ordered the rear 02 sensor and a knock sensor (it did through a code so figured better safe than sorry).  The big question I have is if I disconnect the rear 02 sensor should I be able to clear some of these symptoms temporarily while I wait for parts?

 

Also, if I can disconnect to clear some symptoms, what kind of problems may I run into with it disconnected?

 

Thanks.

Edited July 18, 2015 by lstevens76

[Fairtax4me]

The rear O2 sensor won't cause driveability issues. It's just a check sensor for the converters.

 

It sounds more like you have a vacuum leak, or a bad IAC which is common on that engine.

 

Another thing that can cause rough or unstable idle is a bad MAF sensor. There was a recall on the MAF for a few years around 99-01 IIRC. I had one give me fits on a friends 99 forester. At idle it was reading high which threw off the idle fuel mixture. Drove fine once it was moving, but had a hesitation just off idle when trying to accelerate from a stop.

Look at MAF flow at idle after warm-up. Higher than 4.0 g/sec is too high.

[lstevens76]

From all the reading I have done if that sensor is throwing mixed signals it can cause the system to go in and out of open loop and closed loop as the readings go in and out of range. 

 

Along with this the OBD2 Scanner I'm using is showing ranges on the O2S12 from .1v to .8v.  Subaru FSM says: 

 

"Read data of rear oxygen sensor signal using

Subaru Select Monitor or OBD-II General Scan

Tool.

: Is the value fixed between 0.2 and 0.4

V?

: Go to step 10Q5.

: Replace rear oxygen sensor. <Ref. to

2-7 [W8A0].>"

 

 

I actually see no problems until the car warms up.  It is only after the vehicle is warmed up I have problems and then my symptoms are literally exactly as that person with the Baja described.  

 

From my understanding of the 02 sensors if the ECU reads a spec out of range (regardless of which one) it switches the loop system and uses other methods to adjust fuel trim instead of the 02 sensors.  If I understood the problem the person had (and others have had the same issue that I've read on) it can cause the system to go in and out of each loop.

 

There are actually a lot of threads out there about this, which is why I'm considering disconnecting it (just to see if the problem does go away as well).  Same symptoms, multiple attempts at other fixes, then same solution ends up being the rear 02 sensor.

 

If I hadn't gotten first a P0136, then a P0420 (multiple times), combined with the symptoms I'm experiencing I wouldn't have even gone there.  But when I find multiple posts with P0136 + surging + replacement of rear 02 correcting the problem I have to go with this.

[Fairtax4me]

If that theory is correct, your scanner should show if its going in and out of closed loop.

[lstevens76]

I need to have the scanner hooked up when it's happening.  And I'm not sure how to read that on the scanner, still learning.  If torque would connect I know I could read it on it.  

 

Plus that scanner cord is short so it's annoying to try and keep it plugged in while driving which doesn't help.  I did replace two vacuum lines and then cleaned the IACV which I'm at a stand still now since the stupid gasket deformed and I need a new one and I'm stuck at home.

[Fairtax4me]

RTV around the base works if you're in a pinch. Just don't get it near the pintle. Then allow it to dry for about an hour before starting.

 

 

Most scanners should show Fuel system status in the live data. Should say OL or CL, for open or closed loop.

OL-D or OL-Drive will show under WOT or heavy load.

[lstevens76]

Oh, and I don't have a MAF either.  This is a MAP based system for the '00 EJ222 not MAF so that eliminates the MAF.  I believe my cousin is picking up the gasket for me right now.  If not I'll use the silicone, just trying to avoid the problems that can go along with that.

[lstevens76]

Well we were both wrong and I'm an idiot for not double checking my work. I forgot to fully tighten the throttle cables. The cruise was too tight and the accelerator was lose and floppy.