There are four vacuum hoses on the 1.8T engine that become hard as a rock over time and should be replaced. Three of the four are an easy DIY job; the fourth is slightly more work, since one end is accessed from under the car.
I replaced the three hoses on my 2001.5 Passat with AWM engine with 3.5 x 2mm blue silicone hose--blue, because it looks nice and costs the same as black, silicone because it will outlast the car.
I bought my hose from ECS in two 3' lengths, which was plenty. But if you're doing the fourth hose you'll need more, and 3' might be too short for that hose--but more on it below.
First, don't go disconnecting these hoses to see how they are! They are invariably hard and crack like plaster, so you'll then have a vacuum leak--no good. Get new hose before messing with the old ones!
The four hoses are:
- N112 to Combi Valve
- Intake manifold to N249
- Intake manifold to FPR
- N249 to DV
- FRP = fuel pressure regulator
- N112 = secondary air injection solenoid valve
- Combi Valve = valve on discharge side of SAIP pump
- N249 = recirculating solenoid valve for turbocharger
- DV = turbo diverter valve, aka deceleration shut-off valve
The photos also show the two engine covers removed, but that isn't necessary for this job.
Hose 1 is the longest and toughest to route. It connects to the N112 port that points toward the front of the car (see second picture). The other end connects to the combi valve. If this hose is disconnected you will get a SAIP trouble code.
Hose 2 connects from the port at the front of the intake manifold to the N249 port that points toward the driver (left) side of the car (see third photo).
Hose 3 is short, so you can use a leftover piece from 1 or 2. It connects the intake manifold to the fuel pressure regulator.
Hose 4 is the one I haven't done. It connects N249 to the DV. The N249 end connects to the port pointing toward the front of the car (beside the dipstick tube), so that's easy. The hose goes across the front of the engine then down to the DV, which is only accessible from under the car. On my car (an early B5.5), this hose is a larger OD than the other three, so I suspect the ID is larger, too. It feels much better than the others, so it may not get changed soon...
You can use tie wraps to secure the hoses, but mine felt pretty snug without them (barb fittings) and have been there for months. That should do it!
Intake manifold, with hidden hoses drawn in.
View from left side, coolant tank removed, showing rear half of intake manifold. N249 & N112 are on a plate bolted to the underside of the manifold.