My car has been acting up the last two months (Kia Rio 2016 Auto Gear) it shakes so much when the AC is on at rest only , the rpm also drops and goes up instantly and sometime when the interior lights are on they dim for a second and return to normal , when driving there are no issues until i come to a stop.
I’ll put a link to show how the rpm acts at rest (sometimes it is much worse than that that i have to turn the AC off because it feels like the engine is gonna turn off)
besides above I would also have battery and alternator checked. low voltage will make your vehicle act weird. there is enough voltage with high RPM but not at idle. just a thought
The problem could be anything from a defective alternator which is leaking AC voltage, to a defective fuel injector, to a defective spark plug or ignition coil, to a carboned-up throttle body, to internal engine problems.
Do you have access to a scan tool, even a cheap one, which is capable of showing live data? I had similar poor performance from one of my cars, minus the lights dimming, and ultimately diagnosed the problem as head gasket leakage between two cylinders.
The scan tool I use is a Konnwei KW850, which is an excellent low-cost scan tool. It obviously cannot compare to a $5000 professional scan tool, but for around $70, it’s a good deal. You can get it on Amazon for $69.99 directly from the manufacturer.
Another idea, that could be a vacuum leak of some kind. Vacuum leaks show up more at idle than when driving. Ask your shop to thoroughly check the vacuum system for leaks. Especially the PCV system, and brake booster. Before you take it to the shop you could check for problematic vacuum hoses, broken connectors, etc. If this started after a repair was done, there may be a vacuum hose that was inadvertently left disconnected.
Vacuum leaks often throw a “lean” diagnostic code, so ask your shop to check for that too.
