1.6 16v surging/very low power under load from cold

2007

1.6 16v

98,000 miles

Manual

No CEL and no codes on a universal scanner

Issue occurs on both E10 and E5 fuels

MOT advisory a week ago for a slight exhaust leak due to a loose coupler towards the rear silencer, not sure if this is likely to be related.

On cold mornings the coolant light will flash however the level is perfectly fine but again I'm not sure if that is likely to be related.

I live on a fairly busy road so occasionally I need to set off kind of quick-ish (I'm not thrashing it from cold, 40% throttle max) however this is difficult as the engine seems to deliver next to no power at first. Sometimes it's just very down on power and other times the power will rapidly surge in and out. Once I'm up to the 30 mph limit it's fine, it will accelerate up to the 60 mph limit 1/4 of a mile away just fine and drives normally for the rest of the day. I can't seem to find much about this issue relating to this engine online so any guidance would be much appreciated.

Edited 29 July, 20233 yr by Matt1.4
Added more details.