[Kmb5369]

Hello everyone,
I have been searching the forum for days and can’t seem to figure out my problem.
Forester Information:
2004 forester N/A, 156xxx miles, new denso front O2 sensor last week, new plugs wires and coil pack last year, cleaned throttle body and IACV.
Have scan tool readings at idle when idling correctly as well.
Engine temp-192 degrees
Short fuel trim- -2.3% to -4.7%
Long fuel trim- -0.8%
MAP- 8.1inHg
MAF- .36lb/min
Throttle position- 9.0%
O2S12- .250v to .8v
O2S11- 2.1v to 2.2v
LAMBDA11- around.1
Load_pct- 2.4%
Sparkadv- 10.0

My issue is I am intermittently getting low/rough idle and stalling on start ups. If I remove battery cables and drain off power and reconnect and do idle relearn it will idle fine for a few start ups. Then it will go back to very low idle and stalling again at start up. When it’s at low idle I have to keep throttling it to keep it running. If I push in clutch while driving it stalls out. After a few miles it will start to idle again fine but gets weird when I push in clutch. If I get rpms above 2k and push in the clutch it will step itself down in rpms in 500ish rpm intervals until it reaches 700ish idle rpm.
will start up fine and idle one day and not the next. Recently threw the P0420 code after installing new denso upstream o2 sensor. Have read on forums that this code shouldn’t affect my idling problem? Not sure where to begin in fixing this issue. Also will throw the low rpm detected code when it doesn’t want to idle right and was throwing cylinder miss fire #2 before I changed O2 sensor. Since changing o2 sensor only code I’ve been getting is the P0420.
At my wits end. I know that you guys will have some great info for me.
Thank you all for your help!

 

[Dogs]

Have you checked the actual efficiency of the Catalytic converter?

 

[Kevin]

@Kmb5369 Also are you absolutely sure you got the correct O2 sensor?

 

[Kmb5369]

O2 sensor- Denso #234-9015 says it’s direct fit for 2004 Subaru Forester.

 

[greengoblin68]

I had this exact issue recently on my 2003 forester 2.5x... My forester was idleing around 200 rpms and i had a really hard time starting it.

i ended up removing the throttle body and cleaning it thoroughly, i also removed the iac valve and cleaned it really good with a toothbrush and throttle body cleaner and afterwards i applied 3-in-one oil to the plunger of the iac valve nd to the o-ring. I figured the plunger was getting stuck. new iac valves are very expensive and even if you replace it with a new one it may not solve the problem. But once i was done cleaning everything and reinstalling that fixed the problem.

I followed this cleaning process...
Write-Up on Removing & Cleaning Throttle Body/IACV
www.subaruforester.org/threads/write-up-on-removing-cleaning-throttle-body-iacv.690882/

 

[Kmb5369]

@greengoblin68 Thank you for the info. I will try and tackle this on my days off.

 

[Kevin]

O2 sensor- Denso #234-9015

Appears to be correct - unfortunately they've changed the product codes since I purchased one so I cannot compare.

 

[Dogs]

MAF- .36lb/min

If the calculator is used is correct, this would put it about 2.7 gms/s.

Is this a bit on the low side?

Have you cleaned your MAF sensor?