Vehicle: 2016 Volkswagen Passat Sedan (A33), L4-1.8L Turbo (CPRA), Automatic Transmission/Transaxle

Mileage: 82,908 miles

Problem: The owner brought her Passat to the shop because she was concerned about the idle intermittently fluctuating up and down. The malfunction indicator light (MIL) was not on.

Case Details: The technician connected a scan tool and only found misfire history codes for all the cylinders. At that time, the engine was running normally, so he cleared the DTCs then took the vehicle out for a test drive. Once back in the shop, he let the engine idle for about 10 minutes. After two days of test drives and letting the engine idle, the DTCs did not return, and the engine idled normally.

Finally, on the morning of the third day, the idle returned for about 5 minutes after a cold start. The idle fluctuated up and down before returning to normal. When the technician shut the engine off for about an hour and then restarted it, 5 minutes later, the idle problem occurred again. He was able to duplicate the problem three times in a row that day.

The scan tool showed no misfire counts or DTCs. During the 5 minutes of idle fluctuation, the technician tried blocking off the fuel vapor purge valve hose. He also sprayed brake cleaner around the intake manifold, but that didn’t change the fluctuating idle. He smoke-tested the intake manifold and crankcase but found no leaks.

It was time to call an ALLDATA Tech-Assist consultant to find out what to do next with the diagnostics.

The consultant advised the technician to check the fuel pressure while the idle was fluctuating and to check for an abundance of carbon on the valves. He also mentioned that he had seen the Variable Valve Timing (VVT) magnet causing these types of issues. The little pin in the middle of the magnet gets stuck due to sludge buildup.

The technician tapped on the VVT adjuster, and it popped back to its normal position.

Confirmed Repair: The technician installed a new VVT adjuster. After it was replaced, he took the car on numerous test drives and cold start warm-up sessions. The idle fluctuation did not return. Problem solved!