My first problems began when the engine wouldn't start again if it has been running for over 10 minutes. After it cooled down, engine would start. Next, the engine began surging and stalling. Now it surges so badly, it is like riding a bucking bronco. The fuel pump has been tested at 42 psi. Spark plugs have been replaced. My mechanic suspects a problem with the ignition control module, but doesn't know specifically which part. What could the probem be?