Vauxhall Zafira misfire when cold

Cold start OK, but poor cold drive away for first minute i.e. possibly improves when the lambda control switches in. Appears to drive OK when warm at cruise (light load), occasionally misfires when under partial load, more noticeable on the motorway. Spark plugs look OK (chocolate brown), Air Mass Meter hot wire cleaned with IPA. Next I will remove injectors for spray / flow test. No fault showing on dash Mil light so no OBD carried at the moment. Another area I’m beginning to question is the possibility of a drive-by wire-fault, as the throttle response is may be a little lazy on slight throttle opening.