Rattling noises with a cold engine is usually VANOS. See below


Overview of functions
The double VANOS of the S85 is a high pressure VANOS with oil pressures of up to 90 bar. The oil pressure is created by a separate oil pump. The VANOS oil pump is supplied with oil by the pendulum-slide oil pump.

An adjustment unit each with two VANOS gears is fitted for each cylinder bank. Each VANOS gear is adjusted by a solenoid valve. The solenoid valves are activated by the DME. When running at idle, the adjustment units are at the maximum positions.

Important!

The VANOS solenoid valves react very sensitively to dirt particles. For this reason, ensure absolute cleanliness when working on the VANOS!

Diagnosis instructions
The adjustment of the VANOS is monitored by the DME via the camshaft sensors. Corresponding faults are stored in the diagnostic fault code memory.

If the DME detects control deviations or excessively long adjusting times etc. on the VANOS, this can have the following causes:

Jamming solenoid valves
Solenoid valves can jam due to dirt or metal filings in the oil. It might be possible to eliminate jamming by rinsing with clean oil (oil change).
Important! In the event of metal filings in the oil, the source of the metal filings must be clarified. Jamming VANOS solenoid valves can indicate the onset of mechanical damage of the jamming was caused by metal filings.

Defective activation of the solenoid valves

Defective O-rings in solenoid valves

Insufficient oil pressure
Leaks in the VANOS oil supply or a defective oil pump can lead to a drop in oil pressure. The oil pressure can be checked using a special tool, see repair instructions 11 36 009, 'Checking the oil pressure of VANOS adjustment units'.
Important! During the pressure test on one bank, rough engine operation, misfiring faults and VANOS control faults can occur.

Acoustic problems on engine start (rattling) are caused by a lack of VANOS oil pressure on engine start. Check the pressure accumulator and pressure accumulator valve.