I've got a 1996 960 wagon that I treat very well with 221k miles that I'm trying to drive to 300k.

Most recent history:
Car has been running fine
About a year ago, I replaced spark plugs (will need to check records to see if perhaps it's just time for a full tune-up.)

Two weeks ago, the car started to get a little sluggish from from a stand-still, and seemed to take longer accelerating. Just didn't feel as spirited in traffic or at highway speeds.

I could sense a light amount of surging and falling in power at highways speeds. Then the next day the car started stalling.

Then the CEL light came on, and I rolled into Autozone to get the code read. I believe it was P0103 (high electrical input). This was right when I also needed to do the Texas state inspection and registration renewal. I had my local shop replace the MAF with a new Bosch unit (not cheap, BTW!). The car stopped stalling, but during cold starts it wasn't as smooth as it used to be for half a second, pulling away from a stop was maybe 90% of what I remember, and accelerating on the highway seems to take longer than normal. The CEL stayed off but I had to drive over the course of a few days so the readiness period would pass.

The readiness period passed, the car passed inspection, and then driving home, I took a detour through a neighborhood to check out houses and the CEL came back.

I again rolled into my Autozone near my home, and came away with a new engine code: P0171 System Too Lean

I called the shop to let them know that the light and code returned and I'm planning on taking the car back to the shop, but would like a heads up of what I need to tell the shop because...

the light ended up going off over the weekend.

The car still feels sluggish and hesitates on a cold start. On the phone, they told me they would need to smoke the car to see it it were a vacuum leak. Wondering if anyone has been through this or has a tip. Thanks in advance!