Vacuum Leaks - Find 'em and Fix 'em!
Probably one of the most common problem with D-Jetronic systems is a vacuum leak. Unlike in L-Jetronic, vacuum leaks do not cause a lean mixture condition, but instead cause high idle and idle instability. The problem with finding vacuum leaks is that there are so many sources! Below is a list of some of the more common leak sources:
- Vacuum hoses: Hoses should be replaced every 5 years. They lose elasticity when fitted, hardening and eventually cracking. Replace the entire set with a new set.
- Manifold Pressure Sensor: Cracked diaphragm, leaky case.
- Injector seals: Leaks due to hardening and cracking.
- Intake manifold gaskets: Cracked, poorly sealed and/or torqued.
- Intake runner boots: Leaks due to hardening and cracking.
- Intake manifold (plenum): Can have leaks due to seam cracks and cracks around other fittings.
- Cold start valve: Leaks from the valve itself and the seal to the plenum.
- Throttle body seal: Missing or cracked gasket to the plenum.
- Throttle body shaft: Worn shaft leaks air past the throttle plate.
- Auxiliary air regulator: Stuck open, defective valve
- Distributor advance/retard: Either or both the advance and retard diaphragms cracked or leaky
- PCV Valve: Stuck open or worn out. [Valve not mounted at VOLVO B 20 E/F]
There are various ways to detect these types of leaks. Visual inspection is your most powerful tool, I'm loathe to suggest any other way (e.g. spraying "something" on the suspected part that gets sucked in and changes the idle speed) due to liability concerns.
