have a problem today. hope you guys know what it is. kia forte 1.6sx of 5 years and 4 months old, 77Kkm mileage.
Today the car jerks at idle at red light, and i can see that RPM slight jumps up and down, like 400rpm - 700rpm. Usually it is idle at 400rpm without up and down. The jerk is about every 4 seconds, not constant jerking. can feel the car tremble.
When i press the throttle to accelerate during travelling, the car will jerk again, and does not accelerate instantly as normal. after a while it accelerates to a higher cruising speed, then it's OK again. During jerking, the engine light flashes like 10 times. when the jerk stops, engine light becomes off again. I just changed engine oil and engine filter 2 months ago.
Is this worn spark plugs, or ATF due to change (coz it's been a while), or both, or something else?