99 323i won't start

Sound like fuel problem you can disconnect fuel line before injectors at engine see if their is fuel pressure when you turn key to on possition not all the way to start. Also if you remove rear seat underneath on passenger side is fuel pump you should hear it for just a few seconds each time the key is turned from off to on there is both fuse and fuel relay in your system under hood. I'm sorry I just caught that you were not turning over ..check all your connections at starter and connectors between it and ignition and battery and check your engine to chassi ground basically undo all your conections clean and replace any bad ones with an vehicle sitting for awhile its common

I had same issue, car would fire right up and die almost immediately. I could sometimes make it run for a second or two by giving it gas, but basically wouldn’t idle. Cleaned out the IDLE AIR CONTROL VALVE with some carb cleaner and viola it worked fine. But after I got it running another issue arose with my battery (I think). Now it doesn’t seem to hold a charge? I drained the battery completely trying to diagnose it and fix it and had to jump it to get it going again. I let it run for 30mins or so and took it for a drive no issues. Actually ran better than ever, but after shutting it off at home for a few hours jumped in and it didn’t have enough charge to turn the starter over? I am leaning towards a bad battery, or I noticed my audio capacitor was drawing power and after shutting it off from the audio system, it drained in seconds? Hopefully it’s just wiring, as a battery is not very cheap for this car.