sudden almost complete loss of power and rough idle

[jlg365psu]

I have a 2003 Legacy L Sedan 2.5 It has quite a few miles on it but had been running reasonably well till now. I was beginning to climb a hill when I believe I heard a pop and car quickly lost almost all power. I had to put it in 1st gear (automatic trans) and limp up the hill (barely made it). The car will idle but it looks like the engine is ready to shake off the mounts. To pull out, I have to put trans in neutral, rev engine, then drop into gear. It takes a full block to get rpm's up to speed. I can continue up thru gears like this on level surface and get up to 55 mph, but hills, forget it.

I first suspected exhaust: took heat shields off from header to cat and noticed no issues.

Next timing belt: removed driver side dust cover and belt looks fine

Plugs/wires: I don't think its that because of the initial "pop" when problem occurred

 

I really think that POP is the clue. Please hep me troubleshoot. Should I be checking sensors? Which ones and how?

[Osei]

Question. Have you been running with a P0420 for awhile?

Will it rev freely when not in gear, past 4K?

Any current codes?

Check vacuum and PCV lines.

 

O.

[jlg365psu]

I did not have any codes when the incident occurred. Of course, the "check engine" symbol came on when it happened and has been on since. I don't have the ability to pull codes or get the vehicle to a place that can pull them.

When not in gear, it will rev past 4k but not totally freely. It requires careful depression of the pedal.

All vacuum and PCV lines appear fine and clean.

[jlg365psu]

I have an identical thread posted in the "model specific" -> "third generation legacy" forum. Please continue discussion there. Thanks.