Have this car with the code P0491 already checked the air pump and the solenoid the are both good checked for vacuum leaks none found check combination valves with vacuum gauge they seem to be working and at times vehicle will start idling rough and creates a vacuum coming from the throttle and then it clears up kinda like vacuum leak from the oil separator but the only code that is active is the p0491 my next step is to remove the mechanical valve from the affected cylinder to visually inspect the valve any advice greatly appreciated
I have seen a lot of these with the ports in the cylinder heads clogged or restricted. There is a service bulletin that shows the procedure, and a special service tool that is used to clean the ports. (not a fun job)
Check service bulletin about the ports in the cylinder heads clogged or restricted. Extension waranty 8 years or 190.000 km
I like to disconnect the hard plastic corrugated tubes that flow air from the pump to the valve. Block off the end and leak check. They can crack and cause issues... Also you can manually open the valves and blow shop air through them often if ports are clogged you can tell the difference bank to bank
I just did a VW a few weeks ago from another shop. The shop told the guy it needed a computer and needed to be done at the dealer. The Vacuum lines were crossed on the control solenoid. I spent an hour going over the rest of the system and saw new lines found they were reversed. Have seen damaged lines cause this issue. Also have heard of carbon blockage in heads but have not seen this myself.