Re: 2001 5.4 Expedition Engine running rough, Help!!
Steve, scanning for codes is the correct place to start troubleshooting. The codes you posted suggest faults detected by the system:
P0303 = cylinder #3 misfire
P0171 = fuel trim malfunction bank 2
Although the codes may not pin point the exact problem or component, they provide the tech with a starting point from which to diagnostically troubleshoot the problem. In some cases, a faulty component/sensor will be identified, and the solution is to simply replace that component. If you have access to a Ford factory service manual, you will appreciate what steps are required in diagnostically determining the source of fault codes. What may take us a weekend to solve, is solved by the tech in a few hours, but at $100/hour, the shop is the last place we want to be.
The service history (tunes, etc.) or mileage of the vehicle was not provided, so determining the need of tune-up can't be confirmed, although I am assuming the tech was aware of the mileage and maintenance history. To solve the first set of problems is to correct the conditions causing the LIGHT to appear. If you aren't mechanically inclined, then speak politely with the tech.
"Sulfur smell is usually generated by high temperatures in the catalytic converter caused by excess unburned fuel going through the exhaust. The converter oxidizes this fuel, which generates the heat, and the high heat generates the smell. An occasional whiff of this smell upon start-up or momentarily at idle isn't necessarily a problem. In fact, it indicates the catalytic converter is doing its job in preventing unburned fuel vapors from reaching the atmosphere. But of course, the concern is what's causing the higher percentage of unburned fuel from the engine." From article by Paul Brand.