Do you get a check engine light. I got code 17 which is o2 sensor signal short to pos or ground. Sensor was fine I think it was seeing a lean mix on higher rpm that could not be adjusted for. I remembered another place I once found a vacuum leak it was at the canister(carbon canister I think) in the area behind the plastic fender liner behind the drivers side front wheel. It connects to the connector you are supposed to disconnect and plug when checking lambda