need help car acting weird

[240sx_in_209]

Ok well i got a dual cam s13. just recently the car started acting weird. lets say about a week ago my brother bought a car. had fuel cell it was sorta like a weekend race car that was broken down. well i took the gas from it.. said it was still good it was only a couple of months old. and it was almost a full take that it got me like 12 gallons or so. since then car has been acting weird and im like ok the gas was problem a lot older than that and now its not to good. Now the car kinda bogs down down low. im at idle i step on the gas and the RPM drop and then go up. and now the car is idling like jumping up from like 1300rpm like down to 300 rpm like its about to die.. then the car will die.. it wont stay on it wont idle.. but i woke up the next morning.. and its fine. no weird idle no nothing. only a smell from the exhaust from maybe the gas or it maybe mest up my catalytic converter. Any one have any ideas why it would be doing this. and then all of the suddenly stop, but it will do it at random times

[GrilledCheese33]

If the gas is old, then it probably has a bit of water in it. Go pick up a can of iso-heet from your local autoparts store and that should help it out.