Thats a new one.... Sounds too good to be true..

The vaccum is there to let the EZL decide when to advance the timing based on the amount of vaccum.

More vaccum = Idle or slow moving
Less Vaccum = Wide Open Throttle or fast moving

So pulling the vaccum will let the EZL think that the car needs more advance timing and power thus advancing the timing.

I wonder if the quiter engine you are referring may be due to the absence of the shaking at low idle; in which case increasing the idle will smoothen it out a little....

Hope it helps.

__________________
1992 200E
M102
102.963
AKA Silver Old Grumpy
Always hope I can freeze someone with the aircon- Just change the compressor again, Subseal leaked with a psssssssss sound.
Its the NON-3 Pointed star items on my car that cost more to repair.$%^&%%*^&