Asked in
Spark Plugs and Wires
Kia Rio
Air Filters and Intake Manifolds

What causes 03 KIA RIO to have a very rough idle at red lights and stop signs otherwise it runs so smooth changed the spark plugs oil air filter; nothing helps?


User Avatar
Wiki User
April 05, 2008 12:20PM

While replacing the plug wires could eliminate some of the lost power from the coil pack, the more likely suspect is lost cylinder pressure. In order for gas engines to fire solidly, a cylinder pressure of 100 PSI or greater is required. At lower RPM's this is some times not achieved due to worn piston rings or damaged cylinder head valves. At higher RPM's this will normally smooth out. Reccomend having your cylinder pressures checked at a local shop or do it yourself. The pressure tester can be purchased at sears or your local parts store. Simply remove all spark plugs, thread the pressure gauge into the head at the spark plug hole, turn your engine over for at least 3 seconds, then read and record the reading on the gauge. if under 100 PSI, that is your problem. Good luck! Replace the plug wires. Have the engine codes read. I suspect a random misfire.