If you are investigating an idle speed that rises and falls, save every stored and pending code before clearing anything. Compare commanded and actual idle speed, fuel trims, and misfire counts. Record the engine temperature and load alongside the reading; the same value can mean different things in different conditions.
A basic reader may not access every module. Check for intake leaks, a sticky throttle path, and recent work around the air duct. Use the exact vehicle’s service information to interpret the result.
Quick educational note
For information, not a diagnosis or repair instruction. Vehicle-specific checks are still required. Consult the manufacturer's guidance and a qualified technician.
How to use this information
This article explains general principles and does not establish what is wrong with your vehicle. Read the content limitations.