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I have an 86 240. Last winter, when the car sat all night at -20C, it would either barely start and die, or wouldn't start at all. Usually after extended cranking, or leaving it till the temperature rose a bit, it would finally start, running rough for a few minutes, and then would be fine. At -10C, it showed no symptoms.
I thought at first it might just be a bad ECU temperature sensor, but it met spec. By the way, my car doesn't have a cold start valve. If yours does, verifying its function should be one of the first things you do.
I did a bunch of related maintenance since:
1) cleared clogged hose from flame trap to intake manifold
2) replaced fuel filter and check valve
3) replaced plugs, wires, distributor cap and rotor
4) used a fuel treatment
5) replaced O2 sensor - set 50% duty cycle at test point
6) replaced air filter
When I tried a morning start at -20C recently, it started fine. I'm not certain exactly which of the above cured the problem, since I couldn't test with cold weather along the way. I've put them in priority order of what I think may have fixed the problem though.
Comments:
1) My crankcase wasn't getting ventilated, and eventually I found that my dipstick was getting rusty, presumably due to excess moisture. When I later pulled the plugs, the contacts were rusty!
2) If it's been a long time, a clogged fuel filter could be involved, since cold starts need extra fuel. I couldn't even blow through the removed one; it seemed air tight!
3) The rusty plugs could well have been involved, although I don't recall if I they were this way last winter.
4) I've seen comments that buildup on the intake valves could absorb fuel which is needed most during cold startup.
5)I wouldn't think that the O2 sensor would affect actual starting; more likely, just how it runs after starting.
6) My old air filter wasn't that dirty, so I don't think replacing it was a factor
Good Luck!
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