My ford windstar 2003 hesitates during cold weather or wet conditions. But good during idle. Some time shows blinking engine light.

what code comes up when the engine light comes on

HAVE ENGINE AND TRANSMISSION CHECK FOR CODES

I would check vacum lines or system for leaks

One of the most common causes for the issues you are having, and
something that you may want to check, or have checked is the, ( MAF ), " mass air flow ", sensor.
Some of the symptoms are, bad idle, loss of engine's power, stalling, and eventually preventing the
engine from starting, especially in cold weather.

This is usually easy to check;

The sensor is usually located in the air intake duct system, the duct system that the air filter is in )
between the air filter and the engine. Most have a plug with 4 or 5 wires. Very carefully discon-
nect the plug. If the engine doesn't start either remove the battery cables and clean them very
good, or try to jump start the engine. Once the engine is running leave the plug off and go for a
short test drive to see if you notice the engine performing better.

You can drive while this is disconnected, but try not to do that too long. It can cause other
sensors to trigger the, " check engine light ", and over a longer period of time can damage the
catalytic converter.
Some handy people go to a parts store and get, " mass air flow ", cleaner. It does seem to work
well, but you have to follow the instructions very closely.

I hope this is helpful

overheating, white smoke from tail pipe(ignore this one during cold weather), oil is light brown or milky looking which indicates water in the oil, and of course loosing coolant when there is no coolant leak

good luck worked on these for years, trey replacing the battery isolaters.

Two things that it could be.
1 - Look under the hood, there is a wire coming out of the master cylinder, there was a problem with some of the windstars that leak brake fluid, run down the wires and drip on the neutral safety switch, which would cause the light to come on.
2 - This one solved my problem. It could be the transmission valve body that needs to be updated or changed out. There are many issues with these valve bodies. Slipping from 1-2, OD light blinking, shift 1-2-3-2, late down shift from 3-2. I had all of these.
If you do some work on cars, then you should be able to change out the valve body yourself, with a torque wrench. I picked one up on ebay for $180 with shipping both ways, and took my about 2 hours. My Windstar never drove so good.
-fyi, The OD solenoid is inside the transmission.

First see what #2 spark plug looks like, probably time for a tune up. A compression test will verify engine is in good mechanical condition. Also check the 3 peice intake manifold for leaks - this is common, but ususally the miss smoothes out off idle if this is the case.

Ok, there are many issues here that you will need to inspect. I recommend changing the fuel filter and pump as well. this will fix the hesitation. the intake and exhaust manifold gaskets will need to be replaced as well. this will stop the backfiring.

I also recommend checking and running a teat on the PCV valve and inspect the PCV hose as well. it could have a leak or a small crack on it.

Check the air filter and change if needed. this will help with acceleration issues as well. Next, i would run a check on all plugs and the complete wire set as well. change if needed.

Inspect the injectors for leaks and lose wires. make sure they are in good condition. replace any injectors that isn't firing properly.

Ok, there are some sensors that you will need to check as well. i will list them below.

SENSOR CHECK LIST--

1. Check the O2 sensors for worn wires.
2. Check the MAFS(Mas Air Flow Sensors) Check for Damaged, Loose, or Faulty Mass Air Flow Sensor or Circuit.
3. Check the Air Cleaner Temperature Sensor. this sensor could be damaged ro have loose wires. check accordingly.
4. Check the Throttle Position Sensor. this device could be connected wrong or it may be faulty as well. replace if needed.

Be sure and inspect all the above and repair any problem spot you ruin across during your inspection.

Please rate and god bless:)