1998 Volkswagen Jetta Idling Problem

Hi Bwilli1,

Thank you for the donation.

When engine is unable to idle at cold start, it could be due to a faulty Engine Coolant Temperature sensor.

When idling speed is low arfter warming up, insufficient air is getting past the throttle valve. The throttle valve could be clogged resulting iin insufficient air getting past. Spray some carb cleaner into the throttle valve and use a rag to scrub it clean.

Another possibility is vacumn leakages between the Mass Air Flow sensor and it could be due to cracks in the air hose or faulty PCV,

A dirty MAF would also cause the symptoms described. Use a suitable MAF spray cleaner to clean and retry.