Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
This is Clay, I'm a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description sounds like you have a defective plug wire(s) or a cracked spark plug(s). P0300 is a random cylinder misfire. See if the misfire can be duplicated by spraying down the wire and plug with a light mist of salty water. If need be have someone hold the brake with the vehicle in gear. Again wet down the plug wires one at a time with salty water and see if the misfire can be duplicated or changed in any way to isolate the problem cylinder(s).
You can check the ignition coils by disconnecting the plug wires. 6&3, 5&2, 4&1. The wires that are beside one another and with the engine running spark should jump from one tower to the other. This can be done with the 2 wires from one coil at a time. Kind of a back yard trick, but the spark should jump from one tower to the other clean and crisp.
Let me know if any of the old plugs removed looked really clean, this could be an indication of a cylinder head gasket leak.
I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.Let me knowThanks