Would the cold start valve malfunctioning do this? Sorry to answer your question with a question.
Another thing you may wish to investigate is an air leak downstream of valve. More air coming in makes the idle speed increase. Could it be when the switch was replaced something was moved or not put back on? Or one of the air hoses is brittle with age and has a crack or cannot seal properly anymore?
1989 560SEL (172k)
1989 325IC (122K)
2004 Suzuki Volusia LE (3500 miles)
2005 Yamaha Road Star (20 K miles)