Stock Coil is pretty bomb proof. I've never heard of one going bad (I've heard of a lot of aftermarket ones dying though). HT leads often fail, coil is the block thing that your ignition leads go to (No thats the engine, its the smaller block thing at the other end
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Rough idle is comman and can have a lot of causes. Normally vacuum realated
Underneath the coil is a rubber T piece, check this is intact as it often splits. Also the EGPD valve often plays up
If you give a more precise description of the idle problem, like at what revs, when hot or cold etc I'll have a go a guessing what its likely to be
