I began having an erratic idle about a month ago after cold rainstorm. Idle would swing from high to medium-high, w/ an occasional drop to medium-low (maybe 400-500 rpm). Never stalled once. Acceleration was 100%. If I let it idle for 3-4 min, it indicated fault code 1-1-3 (short term fuel mixture too weak). If I cleared code and just drove (no idle) there was no fault code even after 30+ minutes driving. At the time, Brickboard friends suggested vacuum leak. I checked vacuum tree as well as I could (not exhaustive search) and didn't find anything. Having the good fortune of another Volvo to drive, I put it on back burner until today.

After more than a week sitting, I charged the battery (has 80% full tank). It made an odd sound when cranking, not the "rrr-rrr-rrr" (no gas) or "click-click-click" (dead battery) that we associate w/ many no-starts ... just a weak almost buzzing sound from engine bay. 5 minutes later, though, seemed to come closer to cranking but definitely not sputtering.
I can't help but think the 2 problems are related. Any ideas? Would it run strong w/ great acceleration w/ an ignition problem?
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Two 1995 854 GLT's (w/ manual transmissions)