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2010 - Stall when coming to hard stop! - SOLVED!

42K views 67 replies 11 participants last post by  asealll  
#1 · (Edited)
Back story...

Son's car - lives on his own near me
Owned since 91000 miles
Current mileage: 122863
2.5X with auto transmission
Battery replaced a year ago with high quality battery
Timing belt and head gasket replaced ~6000 miles ago

200 miles ago ( 10 weeks) the car started running really poorly and check engine lite came on. I brought my ODBC reader and saw the permanent codes P0303 and P0304. I researched these but also pulled the plugs and found that 3 and 4 were very suety. Local repair shops had a 3 week wait and Subaru dealer never returned my son's 2 calls so I decided to invest in some parts and a little time. I don't usually throw parts at problems without a full understanding but these codes could indicate plugs, wires, coil packs, etc so I:
  • disconnected battery
  • replaced plugs with properly gapped NKG BKR5EGP plugs
  • replaced plug wires with quality wires
  • replaced ignition coil pack
  • removed and carefully cleaned the MAF sensor as per instructions here
  • oil and filter change
Upon completion, I connected the battery and used the very detailed relearn sequence published in the 2008-2013 forum here ((All Years) - How to Idle Re-Learn after Battery Disconnect)

I took the car out for a test drive and the original horrible running issue was resolved and the engine ran smoothly with plenty of power. However, when I came to a stop, the RPMs would drop to near 0 and sometimes stall or would slowly recover to just above the 1/2 way tick mark between 0 1n 1000 RPM (more on this below). The P0303 and P0404 permanent codes remained but no other trouble codes appeared. (I realize that the permanent codes requires some driving time)

The car sat for 2 weeks due to weather and "life" and during this time I continued to google the issue and kept coming back to the thread above. I went through the relearn sequence again 2 weeks later and now the idle speed dropped significantly coming to a stop but the engine didn't stall, so I thought maybe I just needed to put some miles on it and to clear the P0303 and P0404 codes. I did a 100 mile round trip with a 1 hour stop. The Subi ran wonderfully on the highway (up to 85mph) and on back roads. The idle on brake issue still remained but no absolute stalls - until it was time to return home. Before returning (so after driving 50 miles and sitting for an hour) I checked the codes and the P-303 and P0404 codes were clear and no codes presented - yeah! I then backed up to leave and the engine stalled going into reverse. It stalled twice but I was finally able to back out and get on the road. The drive home was uneventful except for dropping idle speed but no stalls.

So I did some more research and decided to investigate the EGR valve. I tested the resistance on the terminals and electrically it was fine. I took it off and found that it was loaded with carbon deposits. It was the original EGR. For grins I started scraping out the carbon and easy removed 2 heaped tablespoons of very fine dust and some chunks. Rather than continue cleaning I decided it was cheap money to replace the EGR and gasket - which I did yesterday. I left the battery disconnected from the nite before. After installing the EGR I did the relearn sequence again and went for a drive.

I certainly felt like the engine had more pep and I was encouraged. The idle speed did continue to drop but not as low as before so no stalls. And then I noticed something when I pulled into my driveway. As I braked to a stop, the idle dropped to just above that 1/2 line between 0 and 1000 RPM and as I put the car in to Park, the idle speed immediately came up to right below the 1000RPM line and idled nicely. Curious, so I test this several times - putting the car in drive and reverse and then park while sitting in the driveway and this was 100% repeatable. I have a short video of this but can't post it here but here's a link to my hosting site: New Miscellaneous-photos

So, I suspect this is the root of the idle speed drop and stall issue. I've searched but can't find any definitive solutions or diagnostics - hence I'm posting this! Any help, recommendations, and insights greatly appreciated.
 
#3 ·
Excellent question! I don't recall if I had my foot on the brake or not. I need to run an errand in a few minutes so I can take the car and test this.

Ok, so more info. Firstly, if in park, the brake pedal has no effect - pressed or not, the RPMs are their highest.

Also, since this was a cold start I got to pay careful attention to the entire warm up / idle speed process. On start, the RPMs are over 1000 so even going in to reverse had no effect. Nor did coming to a quick stop in that first 30 seconds or so of warm up idle. But as soon as the warm up is done and idle speed returns to normal, then the behavior returns -

in park, idle speed normal
shift in to reverse or drive, idle speed drops and returns when shifted back into park - no stalls in any of these cases

on the road, slowing to a stop sign the idle speed drops and sometimes for a fleeting second several yellow lights on the dash appear but too quickly to read them. I'll try to set up a camera to capture this. But shortly after the flicker, the idle speed comes up so the engine does not stall - but it is below the idle speed when in park.

I did find a post here about checking the transmission fluid - mine is fine.
 
#5 ·
Thanks bman400 - time to do some research on this component! I had not come across the IAC but now that I search it, symptoms do include idle issues (doh).

I'm having a hard time finding a part number for an IAC Valve for a 2010 Subaru Forester with auto and no turbo. Any pointers?

yeah, it looks like this is for earlier models. I did replace the EGR valve yesterday.
 
#13 ·
@mhackney just throwing this out there as something else to look at...

Bobby...
['07 FSXT Member Journal] ['03 X Member Journal]
 
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#14 ·
Well, my fuel pressure gauge setup is specific for Bosch MFI systems. I've searched here and googled and YouTube to find info on how to measure fuel pressure on the 2010 forester with no luck, can't even find what pressure test kit or gauge I need. Granted, I am exhausted after a looong day yesterday but I can usually turn up something.

And just to recap, the car starts perfectly and idles fine when cold. When warm, the idle speed comes down to normal (~850 RPM). But if I then drive and stop, as soon as I stop the idle speed drops and the engine sometimes stalls. If it doesn't stall, it slowly (3-5 sec) comes back up to normal speed and all is good. In addition, I've discovered that if I put the car in neutral or park the idle speed stays normal but as soon as I shift into auto, it drops.
 
#17 ·
When the vehicle is being driven from cold start until a certain point, it is running on what is called open loop meaning the ECU is not making use of any sensors from the vehicle. However when the engine reaches a certain operating temperature it runs in closed loop and uses the sensors to control the engine. And what you're describing seems to match that pattren.
 
#21 ·
Ok, well, I am having trouble finding the knock sensor. Spent an hour searching here, YouTube and even with the factory manual (the line drawings are horrible) I can't be 100% certain I've located it. Here are photos of where I think it and the connector is. Does this look correct?

2010 Forester
Top photo is looking over driver side fender. The blue circle is what I think is the knock sensor connector, the red rectangle is just to provide a frame of reference. My hand is over the EGR valve that I replaced last week.


Is that the connector?
 
#25 ·
Ok, I verified that the photo I posted above is the connector. I can trace the wire down to the sensor that looks like your photo. But try as I might I can't get the connector separated even with a small screw driver inserted. There just is no room to get enough fingers in. I will need to do some disassembly and better lighting later to give it another try.
 
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