Disconnet the battary then the rpm unstable

CHECK IAC SENSOR,CLEAN THROTTLE BODY.

yes every thing is grounded also check your starter. make sure all wires are tight and that the starter is good. also check your starter solenoid

Removal & Installation

1. Disconnect the negative battery cable.
2. Raise and support the vehicle safely.
   NOTE When removing the hard shell connector at terminal -S-, grasp the plastic shell. Do not pull on the wire.
3. Disconnect the starter electrical harness.
4. Remove the upper starter bolt.
5. Support the starter and remove the lower bolt.
6. Remove the starter from the vehicle.
   
   
   Fig. The starter is located at the lower front of the engine, and is visible through the air duct
   

To install:

1. Position the starter in the vehicle.
2. Install the upper and lower bolts. Tighten to 15-20 ft. lbs. (20-27 Nm).
3. Connect the starter electrical harness. Tighten the starter cable nut to 80-124 inch lbs. (9-14 Nm).
   NOTE When installing the hard shell connector, be careful to push it straight on and make sure it locks in position with a notable click or detent.
4. Lower the vehicle.
5. Connect the negative battery cable.

Hope helps (remember comment and rated this).

2003 Ford Truck Windstar 3.8L SFI 6cyl Repair Guide

Ford Windstar 1999-2003 - Starter Removal & Installation

1. Disconnect the negative battery cable.
2. Raise and support the vehicle safely.
   NOTE When removing the hard shell connector at terminal -S-, grasp the plastic shell. Do not pull on the wire.
   
3. Disconnect the starter electrical harness.
4. Remove the upper starter bolt.
5. Support the starter and remove the lower bolt.
6. Remove the starter from the vehicle.
   
   
7. 
   Fig. The starter is located at the lower front of the engine, and is visible through the air duct
   

To install:

1. Position the starter in the vehicle.
2. Install the upper and lower bolts. Tighten to 15-20 ft. lbs. (20-27 Nm).
3. Connect the starter electrical harness. Tighten the starter cable nut to 80-124 inch lbs. (9-14 Nm).
   NOTE When installing the hard shell connector, be careful to push it straight on and make sure it locks in position with a notable click or detent.
   
4. Lower the vehicle.
5. Connect the negative battery cable.

I really hope helps with this (remember rated this help) Good luck.

If you have a standard shift transmission.....give it a push with the key on and release the clutch in 2nd gear to start it.
An automatic will have to be towed.

CHECK FOR LOOSE IGNITION SWITCH BEHIND THE KEY YOU MAY HAVE TO REMOVE THE SCREWWS HOLDING THE STERRING COLUMN COVER ON, ALSO OTHER THINGS IT COULD BE WOULD BE YOUR NEUTRAL SAFETY SWITCH OR THE STARTER RELAY AND FINALLY THE STARTER? YOU WOULD NEED A TEST LIGHT TO DIAGNOSIS? ONE THING YOU COULD TYR IS REMOVING FUSE/RELAY COVER UNDER HOOD AND SWAPPING THE STARTER RELAY WITH A SIMILAR ONE IN THE BOX ? IF IT STARTS THEN THE RELAY IS BAD ? GOOD LUCK

REMOVAL & INSTALLATION 2.0L Engine

1. Disconnect the negative battery cable.
2. Remove air intake resonators.
3. Remove starter motor upper mounting bolts.
4. Raise and support the vehicle.
5. Remove the nuts on the starter terminals and remove the cables from the terminals.
6. Remove the two starter lower retaining bolts and remove the starter. To install:
   
7. Place the starter into position and tighten the 2 lower retaining bolts to 15–20 ft. lbs (20–27 Nm).
8. Place the starter cables onto the terminals and tighten the retaining nuts to 80–124 inch lbs. (5–7 Nm).
9. Lower the vehicle.
10. Install and tighten the upper retaining bolt to 15–20 ft. lbs (20–27 Nm).
11. Install the air intake resonators.
12. Connect the negative battery cable.

2.5L Engine

1. Disconnect the negative battery cable.
2. Remove the engine air cleaner assembly.
3. Remove the fuel feed and return lines from the support bracket located on the accelerator cable bracket, and remove the fuel line bracket.
4. On vehicles equipped with a automatic transaxle, remove the gear selector and the gear shift cable bracket from the transaxle.
5. Remove the air cleaner support bracket from the engine and transaxle mount.
6. Remove the nuts on the starter terminals and remove the cables from the terminals.
7. Remove the starter motor-to-transaxle case retaining bolt at the rear of the starter.
8. Remove the two starter retaining bolts and carefully lift the starter from the transaxle case while disengaging the alignment pins. To install:
   
9. Position the starter onto the alignment pins and onto the transaxle case.
10. Install the two starter retaining bolts and the rear retaining bolt and tighten them to 15–21 ft. lbs. (21–29 Nm).
11. Place the starter cables onto the terminals and tighten the retaining nuts to 80–124 inch lbs. (5–7 Nm).
12. Install the air cleaner support bracket.
13. If removed, install the gear shift selector and bracket.
14. Install the fuel line bracket and install the fuel lines in the bracket.
15. Install the air cleaner assembly.
16. Connect the negative battery cable.

disconnect the battary for aprox 1 hr this will clear the computor of bugs then reconect drive for about 30mins and problem should be solved .
good luck

I have a '95. It's behind the passenger side tire. Remove tire and rock guard if you have one--couple of screws--and you can easily access it. two bolts facing rear of car, two connections up front. Honestly it was the easiest replacement I've ever done. Just disconnect your battery first.

it could be a possibility that it has a faulty rpm sensor have been known to go.