2017 Outback limited 2.5L 4 cylinder 50,000 mi.
When I stop at a light it idles a lot rougher with the A/C on (especially the first few minutes of driving) and occasionally so much that it almost stalls for a second.
It also occasionally almost stalls on start up and barely “catches” then runs, and has not started and needed a second start a few times.
Air filter always changed and new, battery only 2 years old.
I would rather not break down in the neighborhood I work in…is there something simple I could check, or take it to the shop and see if something needs to be repaired preemptively? Thanks
Try this first - cheap, pretty easy and often quite effective.
https://www.youtube.com/watch?v=NWCKvU2FmDc
You could scan it for codes, maybe record live data when you turn on the AC, to see if the computer reports anything suspicious. Rough idle is not a problem with those boxer engines if everything is working properly. Assuming normal maintenance has been done there should not be serious problems at that mileage.
If not for the starting problem being likely related I'd say the AC compressor was wearing out and loading down the engine too much. It's worth checking fuel pressure and seeing if that's up to spec. Has the fuel filter been replaced? Although spark plugs should be OK at that mileage it would probably be worth taking a look at them (a bit of a pain on late model Subarus), as well as checking for vacuum leaks.
You could also clean the throttle body and MAF sensor. Although it shouldn't be a problem at the mileage you could clean the fuel injectors in case you have some clogging going on - maybe try some Techron or other PEA cleaner in the tank and see if that helps, or try the ATS 505 CRF fuel system cleaner that Scotty has talked about in his videos.
Fuel filter has not been replaced. That or fuel pump was my instinct based on how it felt, but I’m no expert. I’ll try your suggestions- thanks
As @glen_stet suggests, do the simple, easy, and inexpensive things first - clean the throttle body and MAF sensor and see if that helps.
@chucktobias has the answer. The bearings on your ac compressor are going out and loading down the engine at idle.
Just checked it out. That disc on the end of the compressor is the clutch and should only spin/engage when a/c is on right? Everything spins weather a/c on or off.