Engine light came on, had a p304 code. Took car for repair, mechanic could not figure out why engine light came on. Cleared light, car started to hesitate when stopped, engine light came back on. Spark plugs checked, engine light still on

SOURCE: 96 Ford Windstar runs rough, check engine light on

Sounds like you have some EGR ports clogged up, remove the intake and look at the egr ports all but
#1 cyl port will probably be at least partially clogged, hope this helps

SOURCE: My 2002 Ford Taurus will shutter and die when

the idle air control valve is responsible for engine idle.
this is a common failure on ford's. but I don't think yours is bad because it does idle high befor it dies.
you stated you had codes p0171 and p0174 these are lean codes for bank one and two, you said you found a vacuum leak and repaired it, the vacuum leak was mostly likely the cause of the lean codes, however the pcm has calibrated the fueling stategy for this lean mixture, what you need to do is erase the KAM "keep alive memory" this is done by unhooking the negative battery cable for 60 seconds, this is the only way to erase the KAM the $6000.00 machine I use wont even do it.

once the KAM is clean the computer will go into a relearn state and all operating values will be adjusted for the vehicles current condition, during this relearn session the vehicle may have some driveability issues (low or high idle, stalling, poor fuel economy) the relearn should complete within 10 minutes of idling and then 10 minutes of driving.

good luck and keep me updated

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SOURCE: Have a 1998 F-150 XLT, 4.6 (6) Windsor Engine.

Could be the coil pack should be read in ohms about 7 to be good

SOURCE: 2002 Ford Ranger check engine light indicating misfire

Code P0301
Ignition Coil Pack
Ignition Cable
Spark plug
Clog or dirty fuel injector
Evap canister purge valve
Engine Compression
fuel pressure

you have 3 type of engine for your truck
2.3L 4 cylinder
3.0L 6 Cylinder
4.0L 6 Cylinder

need to know that type Engine

The reason why the service light come on because it is a hard code
not a soft code.

Let me know

SOURCE: engine light on 2002 Explorer. engine code P1400

This may have to do with a bad wiring. Check all the wiring associated with EGR operation. Whenever a computer throws a code about high or low circuit voltage, it is usually attributed to abnormal wiring.