Rpm Issue?

[exwife's kia]

My ex wife's 2002 Kia Sedona has a freaky problem. When she has the A/C and her radio on and she comes to a stop the tach drops really low. Sometimes causing the oil and alt light to come on. When we look at the 2 indicators on the dash that are on when she is at idle they flash in time to the car's engine speed. when the a/cis off the tach still seems dangerousy low like near the first line. On occasion her XM radio would cut out too. Oh and on top of that the pass head light went out. Here's what we did. I checked the battery with my fluke and it was at 12.58 -13.08 at reast when we started the car it dopped to 10.9 VDC. When the engine was running the alt was cranking out 13.58-14.6 VDC deoending on how long it was running. I still went to auto zone and had them put the machin on the battery and it tested god. We also connected the OBD II and it says no system faults. Any insights she needs the car to cart around the kids. Thanks in advance

[koreatech]

Check the alternator voltage with the vehicle's electrical system loaded, and the vehicle in drive. If it drops below 13.0 volts, it can't keep up with the demand. There is an upgraded alternator from KIA that should remedy this, but make sure you get the proper belt for it.

[ron1004]

Welcome to the forum.

The readings you took with your fluke confirm that your alternator is good - the normal charging voltage is 13.8~14.6 with the engine at normal RPM (+ - 800) and higher - your voltage is dropping due to insufficient RPM's.

To me it sounds like a problem with the Idle Speed Control (ISC) valve - this valve modulates to maintain a set idle speed regardless of load changes such as power steering, AC, and lights.
Most often the ISC problem can be solved by removing it and cleaning it with carb cleaner.