I think, it was end of the 90s, when our Kia Sephia suddenly had a total "twitchy" no-load running and it was tricky to take off. My father didn't wait too long and visited our Mitsubishi/Kia service station after two or three days. Our master mechanic then took the compressed air-gun and blew the air intake through. After that, the motor ran fine again! Obviously, the throttle valve was filthy by anything.