Problems after fitting manifold :-(

Hi guys,

New here, and literally just purchased my first renault.
It's a 57' F1, it's been fine for a week or so then developed the dreaded flexi breaking I've literally just fitted a toyosport manifold and Milltek cat back, keeping the main cat in place. Now I disconnected the battery whilst carrying this out and on initial start up all was fine.
Once warm I drove it down the road, the car was very "flat" and didn't want to idle as normal? I cycled the ignition to try and reset anything and it then seemed back to normal.
Ive since driven the car home from work and under hard acceleration now have a intermittent misfire/power loss that clears after a few second off throttle the part throttle? Is this a mapping issue due to removing the precat? Or symptoms of injectors? It's been driven harder than tonight and been fine?
Any ideas are greatly appreciated
Cheers

Nick
 
is the car mapped to start with ?
if not you will need to get it mapped to run properly with the pre cat out and having a milltek
some clio 197s or 200s are almost undriveable after removing the pre cat