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?
A faulty or biased O2 sensor can cause the condition your describing. It sounds to me like the engine is running very lean and when you restrict its air intake it settles out. Any chance you can get a hold of a scanner an view the data stream? Let me know!