Car Wont Stay Running
 

Hey guys im new to this forum, and i need some help. I have a 98 328is and im having trouble keeping it running wen cold. It has 200, 000 mi and up until recently has ran pretty good. Once in a while if it sits for a few days, when i go to start it up it seems like it runs on a 4 or 5 cylinders, idling rough...after a few seconds to a minute of revving it, it goes back to a normal idle. But now every time i wanna start it, it wont staying running at all unless i rev it for more like 2 or 3 min... and once its warm it still has a little rough of an idle....If i pull the oil dipstick it actually idles better. I tried checking the vacuum at the oil separator and there was sum vacuum..but if i unplug it, it dies.. But i dont get y it idles better w a me pulling the oil filler cap or the dipstick. Im sure its something simple that i cant think of, but would appreciate some help if possible, thanks.

The oil cap is part of the vacuum system. Opening it is just causing a gigantic vacuum leak in your system and the extra air mixture probably explains why it idles better.

Start with the basics first, from things directly related to ignition and work your way down. Inspect the spark plugs and verify their condition. Also have the batter tested and test your voltage output on your alternator if and when you can get it running. Also verify the pressure on the fuel system and replace your fuel filter/regulator if needed. The way you've presented your problem makes it very generalized for a fuel/air/voltage issue. So just start with the easy stuff first to save yourself money on unnecessary parts like my dumb ass does.

I'll try and look around for you and post back here later. Good luck.

sounds like plugs, id check them, if its not the plugs then probably the coil packs

is it throwing a check engine light? if so have you read the codes?