I have a 2000 ranger with a 5.0 explorer motor. truck runs excellent now. I had a hesitation but tuned it up. msd coils, taylor plug wires and motorcraft platinum plugs. the check engine light was on when I got the truck but it was just the solenoid vent circuit malfunction. the wire to the back was broke in half. check engine light stays off now. the hesitation went away immediately after the tune up. but when I stop fast at like a stop sign the rpm's drop and it stalls.sometimes it can catch itself and stay running. it always starts right back up and runs great but very annoying it does this. everything is normal if stop under normal driving. any ideas would be greatfully appreciated. thanks.

 

Could be torque converter isn't unlocking, TCC circuit.

Try shifting to Neutral and then do some fast stops.

Does transmission seem to shift at the right times and smoothly?
Computer needs accurate speed sensor signal to know when to shift and when to lock and UN-lock torque converter


IAC(idle air control) Valve is used by the computer to set idle RPMs when coming to a stop, as speed(need that speed sensor) drops below 5MPH computer should start to open IAC Valve to "learned" position to get target idle for "in gear" warmed up engine.

On cold start idle should be high, above 1,000rpm, then it will slowly drop over the next 5 to 10 minutes as engine/coolant warms up.
If thats not happening then IAC valve may need to be cleaned or ECT(engine coolant temp) sensor may need to be changed or tested

When you shift into gear computer should also bump up idle using IAC Valve

 

I forgot to put in the first post that it does it in neutral as well. everything on the truck works perfect accept for this. I just put a new thermostat in and water pump. according to my scanner everything is working right. The engine coolant temp sensor is working right. I wondered about the iac valve. Everything is normal though when I start it, the rpm's go up like they should. I was reading online about the iac valve, someone else had the exact same problem as me but they never said weather or not they fixed the problem. But someone suggested the iac valve and something about "dashpot". they said something about the iac valve not working correctly. Another time it will quit I recently discovered is if I do donuts on bare pavement and spin around really fast sometimes it will quit just like when I stop fast. I was wondering if that acceleration sensor on the frame rail by the transfer case could have anything to do with it. but that wouldn't affect it when spinning around fast I didn't think. I rarely stop fast enough for it to bother me but still very annoying knowing its not perfect. Stuff like that bugs me.

 

If the truck was ever repaired from a collision they may not have replaced inertia switch, it has a weight inside that cuts fuel pump power in the event of a sudden stop.
Long shot, because engine shouldn't restart until you reset the inertia switch.

IAC Valve is mounted sideways so if valve inside was loose it could slide forward cutting off air in a fast stop, another long shot

 

Fuel pump is weak? Not sucking enough for the bigger engine.