I just replaced my rocker gaskets, and as everything was covered oil i decided to clean the engine(carefully covering the alternator and induction kit + MAF), the car started up first time with no trouble and drove fine, but after driving around for about 1 hour it started hesitating very badly and misfiring under 3k revs,the engine light also came on, but after about 15min it went out and everything was fine, the next day it drove fine but once warmed up it was hesitating and missing intermitantly as well as the engine light coming on and going off, i decided to take the coil packs out and check them out, they all seemed fine no cracks etc BUT one of the tips on one of the coil pcks crumbled away in my hand, i pushed the rubber cap back on then put it all together, at the same time i cleaned out the maf with a intake cleaner, i took the car out for a blast and everthing seemed fine even with a damaged coil pack, i drove the car again today and seemed 100% with no engine light, any suggestions on what i should do, shall i replace all 4 coil packs??the car has done 78k miles and as far as i know they are the original coils...many thanks

 

I'd be tempted to say it was the MAF as they are very tempremental on this model impreza, fingers crossed you solved it when you cleaned it. I had a similar problem on my 2000 and it was the MAF. Personally I'd change the coil packs for piece of mind.
Good luck

 

look behind the batery two plugs might have water in them dry them out should be fine wouldnt think its coil packs

 

didnt read it properly change the crumbled coil pack