Engine computers run in Open Loop(factory pre-set operation) until engine reaches operating temp, coolant temp at approx. 195degF, so in 5 minutes or so of driving.
After warmed up computer switches to Closed Loop, it now uses all the sensors like the O2s, to set air/fuel mix for best MPG.
When you are moving and push the clutch in the RPMs should drop but will stay above 1,000rpms, that is normal, 1,500 seems a bit high but...........I don't have an '03.
When speedometer drops below 5MPH(approx.) the high idle should now drop to the 650 warm idle.
This is an MPG and emissions thing, and was added when Rangers got the new EEC-V computers in 1995, it seems to change parameters for each model year, i.e. 'they' fine tune the best RPMs and MPH cutoff in the software, and they do goof, lol, which is why you might need a software update.
And just as a tip, unrelated, lol, when going down hill leave truck in gear with foot off the gas pedal, if engine RPMs are above 1,200(approx.) the computer will shut off the fuel injectors, this of course saves on gas, and one of the benefits of fuel injection.
With a carb engine you would want to coast with clutch in or be in neutral so high engine vacuum wouldn't suck in extra fuel when going downhill, i.e. using the engine to brake downhill speed.
With fuel injection the opposite is true, using engine to brake saves fuel.
Last edited by RonD; 06-20-2015 at 09:02 AM.