I was having my s2000 test driven by an interested party and they stalled. I wasn't there on the test drive, but they told me that they didn't overrev or do anything wrong, however, the car won't start. I kept trying to start it, while hearing the normal turning sound along with another awkward sound by the intake. After a while and my pressing on the gas, the engine started and the whole car vibrated. After gunning the gas, I got the tach to read an rpm of 4-5k (it seemed to jump to this rpm) while hearing a noise in the intake manifold. It sounds as if a bolt has fallen and is preventing it from firing and then bouncing around when it does fire. It could be backfiring. I have no clue. I shut the engine off in the hopes of preventing any further damage. Any suggestions? I would rather do as much as I can before I have to send it to Honda and pay lots in diagnostics. I have two other s2000 engines that I can get parts from, so that's not a problem.

 

Sounds like an over-rev/ engine damage.