Lately my 82 242 runs rough in the morning only when its been raining out, especially if it sits for a day or so without being driven and it's been raining. When it's cold and dry no problems at all, it starts up and runs great.

It will stumble from 1st and second gear and will try to stall as well till the engine warms up. Once it warms up it's beautiful, I just had my mechanic look at it a week ago. Other than the plugs being black all the tune up items were in good order, plugs got changed but since it's back to rain here it's been stumbling again.

Anything in particular I should check? My mechanic is a great guy but he's not a volvo guy, he's been my wife's family mechanic for yrs and super trustworthy but this is the first non volvo garage I've used since I was in highschool. Would like to save us all some time and narrow it down myself.

Any ideas?