Re: Smokin' 156 Jtd - Cough, Cough...
For the boost hoses... the most common one to split is the one from the intercooler to the engine intake...
Open the bonnt, and standing in front of the car, look to the right hand side, just behind the headlight. This is where the intercooler is, and is covered by a black plastic cover (mine doesn't have this cover anymore as it's not needed). Look for the fat black rubber hose that comes up from this area, across the top of the battery, and into the engine. If it's leaking, you'll see some oil spit debris wherever it's split.
However, if it is split, & you're losing boost, it will throw the engine managament light on (you don't mention this).
If you don't have a light, it'll most likely be the air flow meter that's either dirty or burned out.
Just in front of the battery, low down, you'll see the air filter housing. Follow the black pipe out of the top of it... there you will find the air flow meter (wires plugged into it). Easy enough to remove - just follow the "air filter removal" section from the owners handbook. Even easier to disconnect & see if it improves / worsens things!
Just Sold: 2001 156 2.4 JTD (140) Sportwagon Veloce
Replaced by: 2004 (54) Saab 9-5 2.2TiD Linear Sport
Also own: 2007 (07) Vauxhall Astra Twintop 1.6