Car having prob starting and sometimes it doesnt start

[BlueSRT40]

throwing code p0688 and i noticed it pull about 8 inches of vacumm when it doesnt start and stays at 0 if it does start and once it starts runs great...pissing the hell out of me replaced a few parts checked a few just wondering if anyone has any clues on what it might be or things to check. will appreciate any feedback. I live in the south suburbs of chi if anybody wants to take a look for me.