ok so i have an 81 320i with the 5 speed transmission

i just put a half tank of fresh gas in the tank, and when i try to start it it either wont start, or does start when i give it some gas but it wont idle

does anyone know what could be causing this?
im only 16 so i dont really know much about this car but i can figure it out i think

Not a whole lot of info given. How long has car been sitting? Is the gas in the tank been there for very long? It may be bad. Mixing w/fresh wont help!! you might have to drain and clean the tanks. There are several things to check. Do the simple things first. Change plugs, rotor& cap. Re-time, etc. Check for possible vacumn leaks at the intake. Pull the intank pump to see if filter is clogged. USE THE SEARCH FUNCTION! There is a wealth of info there on just about everything you might need to do to get it running. Above all BE patient. Good luck and welcome to the ranks of masochistic BMW owners.

If the car has been sitting for a long time, your best bet is to replace anything that could go bad. Small wear items should be replaced. Plugs, Wires, etc. Change all the fluids like oil and gas, flush the radiator, etc.

As stated the first thing would be to make sure the gas is fresh and then go from there and begin looking at other things such as the fuel pumps and filter. The in tank fuel pump is locate under the back seat. If you take out the seat, there is a little trap door in there.

Good luck, and have fun. I'm 19 now, but I got my first e21 when I was 17. I'm still learning though.