If a search that has worked well previously suddenly starts behaving badly, often the problem has something to do with a faulty keyword substitution or an inappropriate automatic category navigation issue.
You can bypass many of these sorts of search issues by putting one of your keywords in quotes. This forces eBay to bypass the "smart" features and to search for the literal keywords without any substitution or category switching. You may have to manually specify your category once again.
Try this as a starting point:
https://www.ebay.com/sch/i.html?_from=R40&_nkw=%22corvette%22&_sacat=220
