Here is a mini real repair experience on Audi A6 engine vibration when starting car.Hope this article will bring some enlightenment to your work.
Vehicle information:
Audi A6 1.8T made 2011 with 70+ thousands miles.
Trouble Symptoms:
1. Every morning,starting the car with cold engine vibration about 10s~15s,then running normally.
2. Engine run normally at idle.
Engine Vibration When Starting Trouble Diagnosis:
Technicians perform checking as below:
1. Use diagnostic tool read the trouble code,but there is not any trouble exist.
2. Clean the throttle body,injectors and intake pipeline,the trouble is still exist.
3. The idle and high speed exhaust are normally by exhaust gas analyzer.
4. Replace ignition coil,spark plug,water temperature sensor,even ECU still can not solve the trouble.
Technicians get into the trouble,what result in this problem?
Why I replace so many parts,but still can not find out the trouble reason?
Our technicians analyse the trouble symptoms,and believe that:
It is not always idle control error result in engine vibration,it most likely resulted by dripping or oil leakage on the spark plug after a long time leave unused.After engine starting,the oil on the surface of spark plug will volatilize within 10s-15s,then engine work normally.
In order to verify this guess,clean the spark plug and install them back,start the engine at normal temperature,then turn off the engine.Next day morning,remove the spark plugs to check,technicians found the spark plug of number 1 cylinder and number 4 cylinder were wet.And the oil on the surface of spark plug is engine oil instead of gasoline.The cylinder cover engine oil flow through oil seal and valve pipe to the spark plug.Clean the spark plug and install them back,starting the engine without the vibration.
Engine Vibration Solution:
Disassemble the cylinder cover,replace the valve oil seal and re-grinding valve.Start the engine to test trouble and found the trouble symptoms disappeared.