I have a 75 280Z. Latly it has been running like crap. when i start it it idles, at about 500 but fluxuates alot, the tach is not stable. then i give it the gas an it spits and sputters and backfires then straitens out. Sometimes it hesitates to at like 3000 RPM it stays there for a second then will keep revving up. what is going on. o yeha it also jerks alot when its cold like i cant drive a stick but its not that.

You say the tach is fluctuates. If the tach moves erraticly, seemingly not in sync with the engine's actual speed, try cleaning the connector and terminals at the IC ignition unit on the side of your distributor.

no its not the tach that is bad, that is what the motor is doing too.