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Old 01-12-2018, 01:59 PM   #1
888
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Default Stalling on 2012 2.0 after battery replacement

My son has a 2012 Impreza Sport with the 2.0 NA and we recently had the battery replaced. Since replacing the battery, the car runs fine but will occasionally stall when he approaches a light with the clutch pushed in. Meaning, the rpms drop directly to zero versus dropping to, and maintaining, idle speed. This was never a problem before replacing the battery but it's a problem now and is increasing in frequency.

Here is the rest of the story, as Paul Harvey would say. I initially thought it was the starter because the solenoid chattered and the battery voltage was 12.58v right after engaging the starter a number of times on a -5 degree day. Yes, I should have checked it with the starter engaged but I've never seen a battery bounce right back like that.

So I decided to replace the starter but couldn't manage to get to the bolts before my hands went numb and it got dark. I did manage to get the electrical connection loose and I stirred everything around the back of the engine trying to get something on those starter bolts from the top. I gave up, reconnected the electrical pigtail to the starter, and had it towed in to replace the starter, and they determined it was the battery. So it never ran after I was back there messing with the starter.

That's the only other thing that has happened between the "stall and no stall" situations with the car.

I remember this happening once on another car and it was an idle stabilizer valve with a vacuum connection but I don't remember seeing anything like that near where I was working but it was dark when I was out there and I don't work on that car at all.

Any ideas would be appreciated, we've parked it till I can sort it out and it's supposed to snow tonight and I'd like to get him back into the car.

Thanks
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Old 01-12-2018, 11:58 PM   #2
Charlie-III
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Your old car likely had a IACV (idle air control valve) if it was fuel injected and cable throttle.
I believe your son's car is DBW (drive by wire), this no cable to the throttle body and no IACV, the ECU controls the idle.
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Old 01-13-2018, 08:19 AM   #3
888
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Quote:
Originally Posted by Charlie-III View Post
Your old car likely had a IACV (idle air control valve) if it was fuel injected and cable throttle.
I believe your son's car is DBW (drive by wire), this no cable to the throttle body and no IACV, the ECU controls the idle.
Thanks for the reply. Is it possibly a matter of the ECU relearning parameters after the battery change? I looked around the engine compartment last night and I don't see anything I disturbed.
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Old 01-13-2018, 09:03 AM   #4
Charlie-III
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Could be the ECU relearning, you lose fine learning when clearing codes or removing power to the ECU like during a battery change.
This should not take long though, at most a few cold starts unless you have some mods or possibly failing/worn parts which may make it take longer.
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Old 01-13-2018, 09:56 AM   #5
Elbert Bass
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As mentioned yes, your model has "drive by wire" The throttle body is controlled electrically by the ECM. Idle is managed by opening the throttle. As the throttle plate builds up deposits from the crankcase breather system the ECM compensates by opening the throttle a little more and memorizing that as a base setting for initial idle.

When a battery is disconnected or replaced (or engine code memory is cleared) this memorized value is lost. When the throttle is very dirty there can be instances the idle does not relearn. This is why cleaning the throttle body (most shops perform an induction cleaning service) should be performed. We perform them at every 30,000 miles and that seems to keep the throttle clean enough to avoid issues like you have.

Assuming you have not left any of the vacuum hoses loose you just need a throttle body cleaning and clear the ECM memory (disconnect the battery). Unlike earlier models your 2012 FB2.0 will not need to sit and idle to relearn beyond a couple minutes.
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Old 01-13-2018, 10:23 AM   #6
888
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Thanks for the replies.

There are no mods, this is a one owner car we got from the local Subaru dealership that came in on trade for a new Subaru. The guys at the used car center are buddies from our local VW club and they indicated it was well maintained and a solid car for my son.

It had 100k miles at the time and they performed a 100k mile service when we bought it, it has 122k on it right now. It wasn't having this problem before the battery change as per my son so it's tied to that versus anything that had been failing.

I think he drove it home, drove it to work, and was on his way out to dinner when he called me about it stalling. Maybe 5 or 6 starts, most of them cold?

As mentioned, I went through everything on the engine I could find that was vacuum related and it's all undisturbed. Everything I've owned has been the older version of the 2.5 (except the wife's 2017 Forester 6MT which I haven't done anything to yet) so I don't know the 2.0, other than its super slow. I gave everything in the engine compartment a lookover and I did see a small buildup of dirt or sludge around the ground by the fuse block on the strut tower so I took that off, cleaned the body and the ground loop with scotchbrite, and reattached it.

I changed the oil and I'll drive it sometime today and see what it does. The throwout bearing is making a little noise so I'll have to deal with that at some point, too.

The dealer is quite a ways from here, my wife has a 2017 Forester 6MT and I usually try to do everything routine myself and keep receipts. If you guys thing the throttle body should best be cleaned by the dealer, I'll call them and make an appointment.

Thanks again.
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Old 01-13-2018, 03:02 PM   #7
Elbert Bass
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Quote:
Originally Posted by 888 View Post
Thanks for the replies.
------SNIP-----
If you guys thing the throttle body should best be cleaned by the dealer, I'll call them and make an appointment.

Thanks again.
Not all dealers perform induction services at major intervals. You are due for your 120,000 mile maintenance which is safety inspection, air filters, spark plugs, brake fluid flush, and of course oil, filter, and rotate tires.

You can perform the throttle body cleaning yourself. Remove the intake boot from the throttle body. Get a toothbrush, a rag, and some brake cleaner or carb/throttle body cleaner. Wrap the rag around the toothbrush, saturate with cleaner. Stick your finger in and open the throttle plate (there will be spring tension) and while holding the throttle open scrub the top and bottom of the bore and throttle plate. Re-wet as needed, if the rag is real dirty re-wrap a cleaner side of the rag on the toothbrush. Follow spraying some cleaner in the throttle body to rinse, then reassemble boot. Disconnect the battery, push the brake pedal, then reconnect the battery. Turn the ignition on but do not start. Slowly count to ten and then start. Let it idle a couple minutes and take it for a drive.
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Old 01-13-2018, 05:10 PM   #8
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There is definitely a re-learn of the accelerator pedal zero position in the FB20 engine ECU, as well as the idle training. This takes place over 10 to 15 iginition-on cycles (the engine does not have to be started, so you can sit there and do this in the driveway). This needs to be done with your foot off the gas pedal. This can be seen with an ECU scanner through the OBD port.

However I don't think this should affect stalling on return to idle, if it is due to incomplete idle training.

Has the car been allowed to sit and just idle after starting, so that it warms up all the way? Without touching the accelerator pedal? It may be that the idle re-learn doesn't work properly in very cold conditions, and it can't be performed if the car is being driven.

Of course, it could also be one of the other suggestions...

Last edited by Rymar; 01-13-2018 at 09:27 PM.
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Old 01-14-2018, 07:55 AM   #9
888
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Thanks for all of the information and suggestions. It's my son's car so I'm guessing at ignition cycles etc, I do know it's been run to the point of fully warm a few times but beyond that, I'll have to ask him.

Thanks for the info on the 120k service, too.
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Old 01-14-2018, 08:24 AM   #10
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Had to do this on the wife's car yesterday with a new battery.

2 8mm for the clamps, the clip on the driver side holds the intake tube to the manifold, and the breather hose down below that, with clamp.

Remove the intake tube, use a cloth rag and spray throttle body cleaner on the rag. open the throttle plate , wipe out goo, spray and rotate rag till it comes back clean. reinstall intake tube.

Idles perfect.
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Old 01-15-2018, 10:25 AM   #11
888
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Quote:
Originally Posted by Blktrax View Post
Had to do this on the wife's car yesterday with a new battery.

2 8mm for the clamps, the clip on the driver side holds the intake tube to the manifold, and the breather hose down below that, with clamp.

Remove the intake tube, use a cloth rag and spray throttle body cleaner on the rag. open the throttle plate , wipe out goo, spray and rotate rag till it comes back clean. reinstall intake tube.

Idles perfect.
thanks!
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