Does tone sandhi apply to 成语 In my previous question I found the following about tone sandhi and yī 'one':


  yī on its own or not followed by other tones
  
  yī → yí when followed by a fourth tone
  
  yī → yì when followed by other tones


I would like to know if tone sandhi effects the way that set idioms such as 成语 are pronounced.

A prime example is 一年四季, is this pronounced "yī nián sìjì" or "yì nián sìjì"
Similar as for words, tone sandhi also apply for 成语. So 一年四季 is pronounced as "yì nián sìjì", 一波三折 is pronounced as “yì bō sān zhé” and 一马当先 is pronounced as “yì mǎ dāng xiān”. 一触即发 however is pronounced “yí chù jí fā”.