Bad plug, bad wire, bad distributor cap or bad valve.
it is because it is running on 5 cylenders or 3 cylinders depending on the motor
Igniton System or Misfire
Engine cylinder # 5 - misfire detected
The spark plugs are all that are required to be changed. This is at 100,000 miles unless a misfire is detected by the PCM. The coil packs are located directly over the plugs and supply spark. Most times the ignition is flawless and the engine runs smooth. Error codes will be thrown if the engine misfires.
Need to know the year, so we can answer correctly.
P0300 = random misfire.
Random cylinder misfire
There are 2 fuse boxes: one under the hood on the drivers side, and the other is under the drivers seat... they both have black plastic covers that can be removed without tools.
How about the plug wires? If plug wires don't fix it I'd bet it's the injectors.
The 1990 Chevy Corvette front drivers side speaker cover will need to be removed. Remove the speaker retaining screws. Remove the wiring harness from the back of the speaker.
# 3 cylinder misfire.
Ck your injectors, may have one failing