You have to get a vacuum gauge and check the pressure on your hoses. The vehicle specs will tell you what the proper pressure should be then check the various pressure settings to engage each part. Most of all on vacuum systems it helps if all the hoses are replaced and they are cheap.
Fill a spray bottle with half dish soap and half water. Then spray it on all the air and vacuum hoses. Any leaks will create some good and obvious bubbling showing you what hoses need to be replaced. Replacing them is easy. You can buy the air lines at any auto parts store for fairly cheap.
Check for cracks in vaccume lines. Verify all fluid levels are appropriate. Then look at the plugs, wires, and the carborator. It all appears okay, replace the vaccume lines. An in depth explanation is within the owners manual for replacement.