What Causes a Sudden Increase in Idle Speed While Driving?
2 Answers
The reasons for a sudden increase in idle speed while driving are: 1. Throttle sticking or not closing properly; 2. Faulty idle control valve; 3. Faulty coolant temperature sensor; 4. Air intake system leakage; 5. Malfunctioning air conditioning switch or power steering pressure switch. The solutions for a sudden increase in idle speed while driving are: 1. Adjust or replace the throttle position sensor; 2. Clean or replace the idle control valve and use a decoder to perform a basic idle speed setting; 3. Locate the leakage and reseal or replace the relevant components; 4. Check the timing marks and readjust the valve timing according to standards; 5. Clean and inspect the fuel injection quantity of each injector to ensure no blockage or leakage; 6. Replace the three-way catalytic converter; 7. Remove carbon deposits from the EGR valve or replace the EGR valve.
I’ve experienced this before with my old car—sudden idle speed surges can be scary. It might be related to a faulty throttle position sensor, which tells the ECU the throttle position. If it fails, the ECU might send incorrect commands, raising the RPM. Another possibility is an intake system leak, like aged hoses letting in unmetered air, tricking the engine into thinking it needs more air to balance. Try parking safely and listening for hissing sounds from the engine bay. Continuing to drive with high idle can spike fuel consumption and even damage engine components. In my case, I went straight to the shop for throttle body carbon cleaning—affordable but solved the issue. Bottom line: Don’t delay on highways; early inspection brings peace of mind.
