Rip out your EFI and put on some nice side-draught carbs
NOOOOOOO never never never ditch EFI for puddle dumpers.
it sounds like its lean thats why its worse when its cold
on an afm type efi system the most likely cause is an air leak between the afm and engine.
check all the hoses and vac pipes for leaks.
best way is to spray airostart or similar around manifold and hoses, if revs go up you found the leak
hope this helps