I'll just start by going through the symptoms, because I don't really have much of a theory yet on what's happening...

When it's really humid or after it has just rained, my '84 240 really doesn't like to start. Typically on the third attempt at starting it (cranking the motor for a good 5+ seconds per attempt), she'll finally fire up, at which time she'll sputter for a few seconds and then run smooth.

At this point, I head to the freeway to make my way to work. When the gas pedal is just at the right point (somewhere between 50-75% on the accelerator), it sputters and won't accelerate. Above or below that, it seems to be alright. After the engine has warmed up a little more, it runs totally fine.

I have no idea what is going on. Is it electrical? Is there a bunch of condensation making its way into the fuel system? I just don't know.

 

I had a problem with hard starts and dying on my '90 240 when wet. To diagnose it, I used a spray bottle under the hood wetting down suspected areas til I was able to reproduce the hard start condition. Narrowed it down to my distributer cap. Replaced the cap & rotor (and the wires just for good measure), problem solved.

Get yourself a spray bottle and go at it.

 

Thanks! I'll check it out and see what happens. I think I'm going to retire that wagon from daily driver status, so I'll have some time to give it a closer look... just picked up a v70 yesterday

 

Cap & plugs is where to start. Also check 25 amp fuse coming off of battery for corrosion. Ipd sells a great upgrade for this fuse for about $20 that is water tight. I also had problems with an 89 245 that had exposed wires for the o2 sensor that caused problems when it rained. More closely related to your 84, I had an 86 that had a deteriorating engine wiring harness that was shorting out at the starter due to rain. Inspect your harness at the starter, alternator, coolant temp sensor, and at the firewall at the grey plug for corrosion.