It doesn't give you nearly as many options as on a newer car, but you can at least view and clear faults for the engine and for the ABS ECU. It's also possible to monitor a wide range of sensor values - basically nearly every sensor that talks to the ECU will show up in a measuring block.
Are you seeing any fault codes?
High RPM at idle would certainly suggest an air leak somewhere after the maf, or a fauly ISV. I think there is a trick somewhere in the VAG-COM interface for exercising the ISV solenoid - sometimes a proper clean will also help. Check out all your vacuum lines and hoses (to the brake servo, FPR etc.) and the EGR and crankcase breather system - there is also a black baffle muffler box connected to the ISV that often cracks and leaks air.