Papyrus did some IndyCar games before the IRL existed, I think they were circa 1993 and 1995. They have Wikipedia pages and some links.
Codemasters did IRL games based on 2002 and 2005, IIRC. 2002 was a good sim but I remember it looking terrible graphically. 2005 was a definite step up and looked to be headed in the right direction...but the bottom must've fallen out due to low sales or something. I had both games on the original Xbox.
All that said, I'd like to see a dedicated IRL game again as well.Not like iRacing or Grid or Forza 5 but something with the real 2015 teams, tracks and drivers and focused on just IndyCar.