Renault Clio misfiring only at low revs - already changed coil

Hi,

I've recently bought a clio and in the first week it worked fine but then after a short trip in the rain, it began to misfire. So i called the aa out and he plugged his computer in and confirmed the fault was a misfire on cylinder 1. We inspected the coil and it appeared it was a budget one - no manufacture markings etc so replaced it with a new 'better' one.
Drove 100 miles down the motorway without a problem but then I pulled into services for a break and when i came to drive again it began misfiring. But it seemed as soon as i went above 2k revs, the problem went. So another few hundred miles down the motorway and there wasn't any problems until i had to slow down and then it started misfiring again...
I am absolutely baffled.
To add, the 'SERV' light is on however after the aa bloke put the new coil in, he ran another diagnosis and there were no fault codes however we couldn't turn the serv light off.
I do not know whether they're related but if anyone could help me I would be very very grateful!
Thanks in advance,

Jasper Mowatt