Misfire
 

1.8litre 2009 astra the car runs great when cold started, after driving for about a mile or two it gets a bad misfire sometimes on more than 1 cylinder, after driving for a bit it goes away in the lower rpms and progressively goes away in higher rpms until its just gone and runs amazing after not sure what the issue could be. I just fixed the fuel pump and its getting good pressure

Codes?

And what are the codes present in each operational mode described?

Why was the fuel pump replaced?

Sounds like it develops a leak with the expanding metal. Intake gasket maybe. Need the codes and be ready to test.

it ended up being the ignition coil pack

How did you diagnose it?

i remember that a friends chevy cruze with the 1.8 was having similar issues and it it solved his problem so i took one off a parts car he had to see if it helped and it did

Works for me