I've noticed that it doesn't spawn unless you have one just like it in your possession so there must be a spot where it's located.
-An Infernus can be encountered relatively early on if one spawns as a competitor (or in the traffic) during Brucie's street-racesThese can be stolen, although killing an opponent and stealing their car will forfeit the race, lowering Brucie's approval rating-Stevie will send you a message that he requires an Infernus to be delivered in his garageLike most of Stevie's cars, it will respawn if taken away, and thus can be duplicatedFind the Infernus, take it to a safehouse, then return to where you found it; you should find a freshly-spawned one you can deliver to Stevie instead-In GTA IV, you receive one as a gift from Bernie Crane after completing all of his missionsThis Infernus always has a small black stripe on the side and will be either yellow or orange-In GTA IV Multiplayer it can be seen driving around the streets of Liberty City-If you drive an NRG-900 around, especially in and around Star Junction, an Infernus should spawn eventuallyTo get an NRG-900, just go to Westdyke Autos, in Alderney-As with most cars, Infernus' will spawn more readily once the player is already driving oneApproaching the Broker safehouse from the southern bridge may be a good way to spawn parked Infernuses near a convenient storing place.
It can- but the percentage is smallDon't worry about it.
