Coil not quite broken

[bigbroony]

My son's Megane has a low tickover.We've changed the throttle body and nothing else shows up on a diagnostic.He's previously had a coil fail( no3 ).I wondered whether another could be on the verge of giving up.A local mechanic said it wasn't likely as it doesn't misfire when revved.I've also read that you shouldn't disconnect the coils singly to check as it can cause damage.
Does anyone have an idea please.

[Rapidshed]

hi its not harmful in a small check proceedure, just means that cycle wont fire etc,

it may be down to maf or lambda and reading low intake/fuel and causing revs to be low, just a guess.

[bigbroony]

It's had a new lambda sensor recently.Wouldn't this sort of thing show up in a diagnostic check?