Just a note after fussing with several fuel injected cars. The fault code is 21 and that form of fault code dates back to the 1980's. It is known as a semafore, if I am right. The first group of dashes is short with a pause and them a longer series of dashes. With the GM units you have a table which lists a number of sources of the fault code. Before you replace the vac sensor look for wiring and connector problems , including a broken or loose ground return, often serving several devices. Keep looking for that manual which should exist giving total coverage.
Edit. I reread that your blink codes are backwards, first number long dashes, second number short. Same end result