86 RX-7 won't start

Buddy has an 86 RX-7 that he's trying to get running. Says he's getting spark and fuel. Said that the vehicle was running before he replaced the stereo in it. (Anti-theft device?) Also has a duplicate key. Lost original. (Possible chipset in the key?) When I was there last it sounded like it wanted to fire up, but just wouldn't completely start and idle. Any insight to this would be greatly appreciated.