I have a 96 ford windstar with the 3.8 engine with 132,000. When sitting at a stop with the vehicle in drive and the foot on the brake the engine will idle fine except every 10-15 seconds will have a slight hesitation or possible miss. It runs fine other than that, any ideas?

A little background, I had pulled the engine codes that were on for quite a while. P-0171-p0174. I fount the vacume leak and repaired it. Replaced the mass air sensor. had a rough idle and replaced the idle control sensor seems to be running good now except the small hesitation at idle.

Your brake booster make have a leak in it. Temporarily disconnect and plug the vacuum hose going to the booster for a test.

BEWARE: you will have no power assist brakes during this test!

Also, take note that the A/C compressor is STILL working in all settings except OFF, and VENT. I have had mine cycle at that rate, in cold weather.
In other words, it works (at least on my '96) even in HEAT only (floor outlets) in Wisconsin winter.
When the A/C compressor engages, it places a slight load on the engine, and you will notice a slight hesitation followed by a momentary slight increase in RPMS.