Volvo Repair: reoccuring CEL issues and nonfunctioning windshield wipers, windshield wipers, weather days

Question
I was driving on a road trip  in my 2004 S60R 6MT w/65000miles and randomly got a CEL, the engine began vibrating noticeably and there was a distinct loss of power. I took it to a [chain bs auto place], it was all i could find and I was in a pinch. They said the cel indicated a misfire and to correct the problem they both installed new spark plugs and replaced the ignition coils on two cylinders. All was well until driving home, approximately 100miles later, I accelerated from a toll booth, not violently, but vigorously and the cel came on again. There was no noticeable issue this time and I was wondering if you had any thoughts as to what might be the culprit before i bring it to a local [chain bs auto place] tomorrow and complain. Hopefully they'll stand behind their work.

Additionally, now two days after receiving the car back from the shop I noticed the windshield wipers no longer work. The headlight  washers still seem to work fine though, if that's relevant. I'm quite confident they worked when I brought the car to [chain bs auto place] as we'd had some rainy weather days earlier and I definitely would have noticed. Is it possible that when repairing the vehicle a fuse was blown or something? I have had to put a couple thousand into the car recently and would prefer to not go broke getting these issues resolved.

Answer
  John, I doubt the wipers are related. Make sure they are just not loose on their mounting posts. See if you can move them by hand. If not, you will have to dig in and diagnose the switch or motor. Of course, check the fuses first just in case.
  Rescan the vehicle. See what the stored code is. If it's still misfire related, then you have cause with them. If it's something new, you'll have to work on that.

Mark