1990 Volvo 740 hard start when cold

car runs fine, gets 25mpg, everything is working for now. last winter (Iowa) it got to where it would not start on cold days (10 degrees or colder). or if it did start, just barely. now when the weather is warm, still takes a lot of cranking to start. once started, purrs like kitten. one mechanic once told me about a cold start valve or "fifth spark plug", located under the intake manifold. could this be the problem?
thanks