Check for air leaks in the intake system: Check

WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Gentle Hissing Sound Heard From Oil Filler Opening

Courtesy of VOLVO CARS OF NORTH AMERICA.

Connect the compressed air hose and adjust the regulator to obtain a pressure of max 0.3 bar .
A gentle hissing sound can be heard from the oil filler opening. This is due to the opening of an intake valve and the leakage of cylinder pressure past the piston rings.

Fig 2: Identifying Hose Connections

Courtesy of VOLVO CARS OF NORTH AMERICA.

Checking components and connectors according to Checking components and Checking connectors .
If a leak is suspected spray a soap solution onto the area.
Bubbles are permitted around the throttle spindle.
Small bubbles are permissible between throttle body (TB) and intake hose (if of plastic). No bubbles are permissible with rubber hose.
Check for air leakage from canister purge (CP) valve. No leakage is permissible.