I have a 240DL wagon. Though generally reliable, it's always started hard in cold weather (doubly so in cold damp weather). Occasionally I have to get a jump-start from a friendly soul just to get going in the morning after a cold night.

Monday morning I drove my car to work, parked it (10 AM), and left it all day. I had no trouble starting it (even though it was low on gas). I put most of a tank of gas in it on the way to work; the weather was cold with rain and sleet on the drive in.

Monday night (about 9 PM) the car would *not* start, even with a jump-start. It would crank over and even start firing as it usually does, but then just as it was about to get fully started, *POW!* I'd hear what sounded like a backfire from the front of the engine. Repeat, several times. Tuesday afternoon (about 3 PM), same deal. It was still cold and damp, but above freezing during the day.

On the off chance that it's just got ice build-up in the fuel lines, I put a bottle of STP gas treatment in the tank today, and one of STP injector/carb cleaner on general principles (the last guy to jump-start it said it sounded like it had a gummy carb to him). I have not tried to start it since then (about 7 PM Tuesday).

If the car starts, well and good, and I plan to give it the standard electrical going-over afterward: plugs, wires, distributor cap. But if not, what's most likely to be wrong and how hard is each one to fix?

1) Bad plugs/wires
2) Bad fuel filter
3) Bad O2 sensor (Lambda-Sond)
4) Clogged carb
5) Timing off (this one I dread)
6) Something else? From my reading online, the above seem to be common causes of this kind of thing, but maybe bricks are special :)

Any good ideas? I have an extra bottle of the gas treatment if I should add it tomorrow, but my thinking is that it should stay in the fuel system and do whatever it does to deal with the water (it's seemed to work well on this car in the past when I've used it on occasion). -- Joe