I’m having a strange set of engine issues with my 1996 850 with 145K miles. About a month ago, I got a P0304 code – misfire on cylinder 4 – several times over the course of a week. The engine appeared to be running OK, though with rough starting occasionally, which seemed to be connected with wet weather. I decided to change out the wires, cap and rotor to try to address this. Things ran beautifully after that for a couple of weeks or so. Then I went out one morning and could not start the engine at all. My thought was, uh oh, I didn’t tighten things up enough with the cap and rotor and now it has self destructed. Not having time to check things out I left it for a couple of days and then tried again after a quick visual check that looked fine. No luck, other than maybe a whimper of a cylinder firing or two. I left it for a few more days, then went out this morning to try again. After some extended cranking, the engine caught, ran roughly for a while, then perked right up. Now it seems to be fine.

Does anyone have any ideas? While my initial thought was a sparkplug wire issue, since I kept getting a misfire on the same cylinder, I am now leaning toward a fuel issue – perhaps unrelated to the misfire problem. Another piece of the puzzle: for quite some time (~years) every now and then (quite rarely) while sitting at idle at a traffic light the idle speed drops precipitously, almost to a stall, then recovers, and all is back to normal for months. That sounds fuel-related, doesn’t it?

I’m hoping these are symptoms of a known syndrome (bad fuel filter? bad fuel pump? bad ignition coil? etc?) that I could try to tackle. I’ll do simple things like plugs, ignition coil, etc, but I am working on the street (no garage) and I don’t have many special tools, so I can’t do everything. It’s hard to bring it in to a mechanic right now, as everything seems to be running and they’ll just say they can’t find anything wrong.