1990 Corvette Idling Problems.

My car  will not idle properly.  I consider properly at 1100 RPM,s plus or minus.  It occasionally will only idle at 400 RPM's and then it wii die. To make it idle I have placed a piece of plastic on the throttle body to keep it from shutting off and letting the car die.  Now it is idling but it doesn't run smoothly, the rpms fluctuate about 200 rpms likE it is either flooded or not getting gas. The service light does not come on.  I have replaced the fuel filter, oxygen sensor, spark plugs, plug wires, cap, and bug, and all 8 fuel injectors, and throttle positioning sensor and the car still will not idle without dying.  Could I have a bad computer? Please respond if you have had this problem.