Stalling at stop signs after replacing battery

2005 Outback 4-cyl non-turbo has been stalling at certain stop signs since I replaced the battery 6 weeks ago. Seldom happens when mechanic is driving. Transmission flush and supposed “relearn” made no difference. Nor did thorough cleaning of throttle assembly. Has good days stalling only once or twice, and bad days stalling at almost all stops. More likely to stall when cold, or on slight uphill slopes. Aamco man doesn’t think it’s a transmission problem. Regular mechanic can’t fix what he can’t experience, despite test drives on 3 different days. What now?

May be a problem with the idle air control valve or mass airflow sensor or coolant temp sensor.

Jesmed, thank you.

The cars I saw a dramatic idle relearn indications on (after replacing the battery) were eary 90’s 2.8 and 3.1 GM’s. After the first start with the new battery the idle would be all over the place for the first 15 min. I just don’t see (or haven’t seen) idle relearn issues on the cars of today.

Has your mechanic looked at TSB’s? perhaps a module reprogram exists for this problem.

The car’s diagnostics would reset after two twenty-minute trips after the car’s battery is reconnected. This is what your mechanic meant by the car “relearning” how to run. Generally the car’s computer will adjust various inputs to maximize the engine’s ability to run well.
The CEL should be lit after that time if there is a condition that would cause the car to stall randomly. The problem would show up as a misfire in one or more cylinders if the codes were checked. But you mention that the car stalls “at certain stop signs” and that the problem doesn’t occur while your mechanic is driving. Is the car a standard? If so, are these “certain stop signs” by any chance uphill? Stalling is pretty common given these two conditions - it’s why you have a handle instead of a foot lever to engage the parking brake. If you drive a standard and have to engage the clutch on an incline from a dead stop, it is a good practice to engage the parking brake to prevent rollback during that uncomfortable second before the clutch engages.
Experienced standard transmission drivers who are comfortable with their cars may not have to engage the parking brake, but it is there for your right hand to use while your feet are performing a pretty tricky maneuver. What you would do is engage the parking brake by hand first, keeping your hand on the parking brake handle and your thumb on the button at the top of the brake handle. In first gear you would let out the clutch while accelerating slightly, and when the clutch engages you would depress the button on top of the parking brake handle and disengage the brake. This prevents the car from rolling back slightly while you engage the clutch on a hill, and removes that need to time everything just right to prevent stalling or a rollback.

So, is the CEL on, do you have a standard, and are you stalling at stop signs that are making you stop on an incline?
The problem is not the battery.
If the CEL is lit, go with Jesmed’s suggestions in the order presented.
Just FYI, the mass airflow sensor doesn’t fail as often as it just gets dirty, and it is cheaply and easily cleaned.

Kizwiki, thanks very much for your notes. Sorry I didn’t say it has automatic transmission. Six weeks ago after I had the battery replaced, idle speed dropped to near zero. Then 5 miles later I gassed up, at which point the check-engine light came on. Drove 20 easy miles, but the fabled relearning did not take place. Next day, mechanic fixed the idle problem and reset the check-engine light, but said the code indicated possible need to replace the throttle actuator, a $600 part. Instead he cleaned that part. And had me come back later to thoroughly clean entire throttle assembly, hoping we’d not need that expensive part. The intermittent stalling at stop signs continues to get worse (yes, usually on a slight uphill), but no check-engine light except for one day last week.
Went to dealer (by which point no check-engine light). Dealer verified the stalling problem, said trans fluid was jet black, did trans flush and trans re-learn, said problem solved. Also said no active codes, but one “inactive code” indicating catalytic converter. Stalled for me at stop light 200 yards later, and continues today intermittently but gradually more frequently. But still not when regular mechanic test drives it, nor when a transmission guy test drove it on Friday. Seems worse early in the day. If I come to a stop very gently, sometimes that prevents it stalling. If I pump the gas when it’s starting to stall, sometimes I can prevent it stalling. Risky at a stop sign of course. If I slip it into neutral when it’s starting to stall, that prevents the stall but only until I slip it back into drive. Every time it stalls, I retart the engine easily, and at that point it’s fine. Driving me crazy.

Our '05 Outback had 170,000 miles. Eventual diagnosis of the intermittent stalling-at-stop-signs problem was said by the dealer to be the need to replace the throttle assembly. But then, oh, by the way, both your head gaskets are leaking so badly you’ll soon be misfiring. (Why? Mechanic said age, and common with Subarus, and maybe the new engine in the Forester might solve that.) And that intermittent check-engine light means you better replace the catastrophic converter before your emission test next May. Proposed total: $5100. And that’s without the $300 to take out the front passenger seat to replace the seat-belt sensor.

Prior problems we shouldn’t have had: front axle replacement (three times). Tires destroyed (eight) due to rear alignment difficulties. And a few others I’ve forgotten. Oh yes, the O2 sensors – first one, then the other.

So we found another solution, and are sadly no longer a Subaru household. We’ll miss it. Thanks y’all for your help.