The engine idles rough and sounds like theres one or two cylinders missing. Replaced all coils, plugs, and wires, and cleaned the egr valve. When I start it cold it runs perfect for about 5 seconds and starts running rough again. The rpm gauge basically flutters and is very boggy when i give it throttle. Anyone have an idea what could be causing it? I'm running out of ideas.

 

Any check engine light or codes being set ?

 

My 2001 Impala was running very similar. The ignition module underneath the coils that the coils plug into went bad. Would work fine when cold but stop working when hot.