I have an 84 Corvette with the 4 + 3 transmission. One day I started it and the RPM's fluctuated between 7 and 13. If I approached a stop light and got off the gas it would cut off. Ive replaced the throttle body sensor and the computer. Nothing seems to help. Does anyone have any suggestions. When the car is started it revs up and down between 7 and 13 rpms.

 

Could be as simple as a dirty fuel filter or dirty injectors.
Before you spend any more money on big things I would try these 2.
Also, could be you fuel pump.

 

It may have a vacuum leak. Get a can of wd-40 or carb spray cleaner and spray around the intake, egr, throttle body, vacuum lines… any place that would pull air at idle. If the idle smooths out, then you have found the leak. Also listen, sometimes you can hear what sounds like a hissing sound when you have a leak. Don't go crazy with the spray! Just squirt one area at a time with a couple squirts each.
You did not say how it runs otherwise. If you have a stumble just off idle also you might have a sticking EGR valve.
Do you have good power when accelerating? I mean pedal to the mat accelerate! If you are down on power, then I would agree with schoon. A simple fuel pressure check could confirm this also. How about plugs? Wires? All in good shape? Start with the easy things like vacuum leak and go from there.

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Cross-fires were notorious for vacuum leaks around the upper plenum gasket. I agree with 99Hd about the vacuum leak. Use carb spray or you can use a piece of heater hose a couple of feet long, put one end against your ear and listen along the edge of manifold and the hose will isolate any vacuum leak you have.[8D]

 

Yes the car does great otherwise. Me and the mechanic will try it. Thanks!