First thing I'd do is get a sample of fuel by disconnecting the fuel filter at the side and running the fuel pump for a few seconds into a clear container and making sure no contaminants come out. At the same time while you're pouring fuel into the container, hold your thumb over the opening (without getting fuel sprayed into your face/eyes just to get a feel for the pressure. While this is not an accurate measure of fuel pressure, you can at least get an idea. If the fuel sprays out past your finger in a fine mist, your pump is good. If you can easily stop fuel flow, you likely have low fuel pressure; get a fuel pressure gauge to verify. While the fuel filter is off, replace it w/ a new one. Reconnect and test vehicle.
You might need a tune up based on the mileage, especially if it hasn't been done before. Spark Plugs and wires are most affected. There aren't many more expendable parts in the '03 Windstar other than as mentioned and the air filter.
one of out users he owns 2003 Windstar and had a similar situation, engine would bog and sputter similar to your description. However, the problem in his case was a speed sensor which was not engaging with the transaxle turbine output shaft gear. Check and see if while you are driving that your MPH gauge is steady or fluctuating wildly. In addition, activate your Cruise Control on a level surface void of other traffic. Lightly put your foot on the accellerator pedal just to feel it move (no pressure on pedal). If the pedal is vibrating or hunting for position, this is a good indication that the VSS (spd sensor) is not receiving a good signal and needs to be diagnosed. Unfortunately in his case, it wasn't the speed sensor which wore out. The turbine shaft gear was the culprit and the entire transaxle needed to be removed in order to repair. Needless to say, the transaxle was rebuilt while it was outside the vehicle.
You may ask "what is the relevance of a VSS to having the engine sputter? Well, the transmission control module communicates via network with the (PCM) power control module (tranny talks to engine computer) and tells the PCM how fast the vehicle is travelling. Based on this information, the PCM does engine load calculations, compares it to other input sensors, and then determines stuff like ignition timing and fuel injector pulse width. If the VSS is out of range, the PCM cannot accurately keep the engine running, and things get whacky.
If the scan test shows lean error code, or engine running lean, due to low fuel pressure.The fuel filter and fuel pump both are causing this problem.
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Water in fuel can also cause this stutter issue.
Another possibility is vacuum leak.If all checked ok, then get the vacuum hoses checked, if the vacuum line is cracked or any of the vacuum hoses got loose or worn out, them it has to be replaced.-
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