I have a mixture of antifreeze and oil that started leaking on the ground. I don't know what to check. It's a 2002 Kia Rio. Any suggestions?

Random misfires could be gas related- low fuel pressure, vacuum leaks or air leaks upsetting the air/fuel mixture ratio, clogged air filter or fuel filter. Could be ignition related- worn spark plugs, possibly. Or could be an internal mechanical problem-possible valve train malfunction.
Start with a fuel pressure test. check vacuum hoses for leaks, check intake manifold and throttle body assembly for leaks. If you have an exhaust leak at or near the engine, can cause misfires. Air going into the engine is metered by the mass air flow sensor in the big air boot on the throttle body. If extra air gets into the engine through a vacuum leak or a loose hose, the engine computer won't know it, so the air/fuel mixture will be too lean, resulting in misfiring. Several things to check-good luck.

you have to see the tube of air or the air mass sensor

Age of vehicle would suggest a Multigrade 15W/30, such a Castrol, with a replacement Extended Service Oil filter.If you are in a cold weather area, and do a large amount of Stop/Start , or Short distance motoring. The OIL and Filter should be changed, after no more than 4ooo miles of operation.
Regards,DT

check for a bad tensoiner or bad stationary pulley

The water seems to leak out when the engine is running and so it is important to hve the test done when the engine idles.
So fill up and lett it idle to checck if the fault appears.
It is possible that the radiator has got a microscopic leak and is steams out at some stage for sure.
Once confirmed you wilI have to get teh radiator checked with a pressure test. check the bandages of the hose to water pump/engine.
Also the last point if the engine is heating up to oerflow off when it is running and at stops.

either , spark plug seals (in the valve cover),
or spark plug tubes are leaking at the thread (they threaded in to cyllinder head)

ck for a open ground at the pcm

ur cap gas is loose try to buy a new one for sure

check the fuel line hose near the fuel regulator for wear as they tend to leak or corrode causing a gas smell inside the car. My 2000 Kia Sportage just had the same problem with the gas smell inside the car.