1996 Cheverolet Z24 2.4L sputtering/missing

My '96 Chevrolet Z24 5-Speed w/ 150, 00 miles began to sputter/ miss underload until it reached 1800 rpm, then would pull strong. Now it does it constantly. I replaced the fuel regulator, plugs and coils. The cat is not plugged. If I put my hand over the throttlebody to try to "choke' the engine, I can get it to idle smoothly. I replaced/ checked all vacuum lines and there is no intake manifold leakage.
Where do I go now?