Viognier can be a bit of an odd duck. Like Riesling, it can get some of those weird petrol/gas like aromas, and that’s just natural, from the grapes. Like Sauvignon Blanc, it can also get reductive, especially when aged in closed-off situations like you describe. It’s possible it needs a racking or that it even might benefit from a small copper sulfate addition. Always do bench trials here. That’s not the answer if no improvement is noted.
You also might want to try fining to help your Viognier drop its turbidity and fall bright, which can often clean up aromas too. If you don’t mind using animal proteins, one that has some nice effects in white wines and can really freshen up aromas is Gelarom from Laffort. I know it’s so hard to do bench trials when you do such small-scale winemaking, but if you’ve got the tools to measure out teeny amounts of liquids like micropipettes (and I wish all winemakers would invest in these, as well as a gram scale that measures to the 0.01), you can do fining trials in as little as 50 mL wine.
You could always try to blend in another wine to give the aroma a lift. Good matches for Viognier are other Rhône varieties like Roussanne or Marsanne; even Chardonnay can sometimes work as well. You guys and gals know I always say “Never blend a loser” . . . but sometimes even 1% of something else can really make a big positive impact. Good luck!
