i think your on to something Will and it's not that uncommon of problem . Back in the analog days it would have been easy enough to check the Diode bridge ,the Idle RPM , Ignition timming , Or a vacuum leak . today this situation can be a long road to an exacting solution . However , the Internal combustion reciprocating pistion power plant still has the same components , just arranged in a diversified manner . First ; your verbal description of your hiccup is a bit scant in a few areas . Let's see if we can fill in those holes . I will assume that all mechanical components are in
reasonable condition for a 16 year old vehicle . and that maintenance of critical areas has allways been ahead of schedule so any and all repairs have been serviced by qualifyed technicians . OK , HERES my prediction , Where do you buy your gasoline most often ? National brand ? Cut rate ?
Blend Grade ? Or last but most likely the cause , casey's general store ? Blend grade fuels are the most widely produced in volume therefore when the weather changes the volatility requirement of the fuel also changes for optimum starting , Idling cruising economy , power ,etc. it's impossible to keep up ! the volatility of gasoline fuel is dictated by it's REID Vapor pressure a scale measuring the rate of evaporation of a given volume of fuel under controlled conditions such as temerature ,humidity Dew point , etc . all these things wreak havvoc in a cars engine and they change the way in which the fuel reacts in the motor . My end point (yea) check your throttle body where the blade seals in the bore at idle . IS IT CLEAN ALL THE WAY AROUND THE BORE ON BOTH SIDES OF THE BLADE ? iF IT'S NASTY WITH GRAY GOOEY GUM ( FROM CUT RATE FUEL ETC. ) WE NEED TO CLEAN THIS UP !. Throttle body cleaner will do the job quite well but thats not the only area that will cause you trouble . THE IDLE AIR BYPASS RESTRICTION IS WHERE IT'S AT . aND IT'S NOT WHERE THE THROTTLE BLADE IS . THERE WILL BE A CHANNEL OFF TO ONE SIDE THAT LEADS TO WHAT APPEARS TO BE A SOLENOID or electo magnetic thingy screwed in the side of the Throttle body . Off idle troubles are normally throttle blade oriented while idle only problems can be a ISAC(idle solenoid air control ) issue. How does this work ? at idle the ISAC is open and all air to run the engine at it's preset idle speed is run through this channel and mixed with fuel . this restriction on junk gas will turn tar brown to black in color and will normally consume a whole can of TBC,, THROttle Body Cleaner to get it rightous again .As gum and varnish build up in the restriction ,the amount of air metered into the engine decreases while idling only . thus the speed at which the engine operates while at idle will be lower by a slight amount . and as this house that jack built continues to cascade down the hill the alternator output at a slightly reduced speed will be somewhat less
It may not show up on your gauge without an electrical load o cause the alt to ramp up the output to match this load but at reduced rpm's the alt is unable to match this load or as in your case even keep up . unless youv'e got a bad regulator or diode trio or whatever the output without load could read close to 14 but factory gauges are a shot in the dark . A bad ground any where or dirty terminals ANYWHERE IN SERIES WITH THE ALT, BRAKES ,OR BATT. COULD CAUSE THE SAME SYMPTOMS . At night do the headlights dim when the brakes are applied EVERY TIME ? tHATS ELECTRICAL , MOST LIKELY ALT OR BATT . BUT IF THIS LUMINA HAS A FACTORY TACH . WATCH IT WHEN COMMING UP TO A STOP . problem ? yea my tach is electric and when the volt meter drops so does the accuracy of all instruments operating withing the low voltage !!! worst case ,
dealer , have him start with most obvious and work his way backwards . Hey at least it's not a new car , they tell me the hoods don't even open unless you got permission !! Good luck ,, WINDY.
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