2000 z24 with 98 2.4L engine

My engine runs fine at idle with a small valve chatter from old age. The problem is while driving the RPM's drop just like you turned off the switch. Sometimes it will pick right back up other times you must coast to the side and restart. this happens in all driving situations accelerating, at red light or on the highway. I have recently replaced the fuel pump and filter and the crank position sensor. Help if you have any other ideas.