The Phirm Unit 2 Winkworth Business Park, London Road, Hartley Wintney, Hook, Hampshire RG27 8WP 01252 842 872 Give them a call, Discuss your needs with Paul.
The only things that can attribute to the noise difference is something in the air tract ( could be the intake manifold ); but is more likely that because OBD2 has a FAR better ignition control, This will be heard in exhaust note.
If wouldn't drive the car in boost if I were you. Increasing fuel pressure will do nothing. The standard ECU runs a closed loop wideband system, which if not tuned for FI will run too lean, on top of that ignition will be far too aggressive.
look at block 99 in vag com, box 4 should say on, and box 3 should show a trim. All on warm idle, what are the values. If a lambda probe is fitted, and working, idle will be 14.7 AFR
You need to monitor fuel rail pressure to diagnose this properly. At WOT rail pressure should be base(FPR) plus boost. So if you have a 3 bar FPR and run 1 bar boost, the fuel pressure should be 4 bar.
Cruise control was available, but it is not an electronic affair. Due to the VR6 having a cable operated throttle body, an electronic option was not possible. VW got around this by using a vacuum system. The fitting is cumbersome and hard to come by.
With no lambda probe fitted on this system. Idle fueling will not be at 14.7. Its inherent to how we map this system. Fit a lambda probe and you will have closed loop (warm) idle control at 14.7 and what ever AFR in boost that you want by adjusting fuel pressure. Right now if you had a lambda fitted at 90 degree C your idle would be at 14.7, and at 1 bar of boost 12:1. Then if you adjust the fuel pressure to be greater, you'd still have 14.7 at idle and less than 12:1 at one bar boost. Can you show pics of how your dump valve is fitted?