um, i know a lot about cars, and i've never heard a procedure called "smoking" the engine. Perhaps they meant a seal or hose had ruptured? And they used an aerosol to find the vacuum leak? Love to hear what they wrote on your service ticket.

FYI, most auto parts stores have what's called a "code reader," which they will do FOR FREE, they plug it into the car at a special port under the dashboard and it tells them what the engine computer says about the Check Engine light. They can also sometimes clear a non-urgent code, and then you can drive it and see if the code comes back.