My problem is that sometimes when my Astra G tdi 1.7 2002 is idling (is not in gear) the RPM will go to 5000-6000 with out me stepping on the gas pedal. The engine accelerates on its own while idling. I tried reading online and found a post that this could be because of the Idle Air Control Valve. I told this to my mechanic and he told me that my car and diesel engines don't have Idle Air Control Valve. My question is first do diesel engines have an Idle Air Control Valve and where can I locate it on my Astra G?
This is an image of the engine:
BTW, the mechanic has no idea what the problem is.