Apologies if this is old ground but by over revving, I guess you mean a high or inconsistent idle.
Worth a try at a soft reset: Turn ignition on (without starting) count to 90 then start. This resets some of the parameters and often sorts out the problem (temporarily at least).
Did you inspect the underside of all the inlet trunking? It can look fine on top but be spilt badly underneath. Check that there are no possible leaks anywhere between the air filter canister and the throttle body.
After that, get AlfaDiag. Its well worth a one off investment over possible multiple trips to a dealer/specialist. There is a target idle speed parameter which you can reset and you can see any fault codes recorded.
The other area that you can investigate is the idle speed actuator on the back of the throttle body. Not too tricky to change but make sure you don't loose the "O" ring. You will need to reset the ECU afterwards which is why its best to get Alfa Diag first. When I changed mine, tickover was at 2,500 before resetting.
GTV and Racing Driver