I have a small block Chevy with a demon carb. I Have the vacuum tank hose, trans modulator hose and brake booster hose going to a connector screwed into the back of the manifold. Idle is a little rough. I was messing with my car yesterday and forgot to plug the modulator hose in and the engine was running smooth. When I plugged the modulator back the idle was rough again. Any suggestions on why this happens? Mahalos.