I just changed the plugs on the 2.4 (non-turbo) with the Bosch double electrode non-adjustables and I'm getting some stumbling under load and after 50 miles or so, a check engine light . Does anybody have any experience with these plugs misperforming? Pretty sure I didn't mishandle them or drop them. Is there a simple way to test the coils before I take it in to get the codes read? Just to be sure, I'll go out and pull the plugs to make sure the gaps match. The loom was pretty toasty so I replaced that. Is there a particular wire in the bunch that tends to fail? Sorry for the multiple questions, but Volvo is all new to me.