There can be many reasons for this.
Have you had somebody ( Autozone does it for free) check for error codes?
Why do you "think the spark plugs are gone"?
When was the last time a tuneup was done? Fuel filter, air filter, plugs, wires,...
The exhaust leak might trip a code, and/or make the car run poorly, as this is changing the exhaust content that the 02 sensor sees, so the car makes adjustments based on faulty information.