desperate, sudden lack of power on 81 320i

[nbinnm]

Damn I need help . its my daily driver. I returned home from work, next morning the car had trouble starting rough idle, backfire, and 2500 rpm max. I replaced the coil , fuel pump and fuel filter. at some point we removed the air filter and manually with I extended finger I pushed open the large round valve just inside this made I huge difference with the rpm. SO what is causing the trouble. sensor vacuum line what I am desperate. by the way I now have the car a shop and they seemingly have no clue. plz. if you have any ideas .... thx. ,,,, nick

[Jeroen]

All of a sudden huh? One day fine, horrible the next day. I'd suspect a vacuum hose that came loose or burst open indeed like the large intake boot or one of the hoses connected to it. You see this more often but usually that is after being neglected for years. Do a thorough search on the intake side and spray some brake cleaner around. Oil dipstick in there as well? And to be sure always inspect dizzy cap and rotor arm.