Page created by T April 2nd 2012:
One cause of surging has been found to be the Vacuum Tree being loose. This creates an Air Leak in the Inlet Manifold that increases or decreases as the Engine moves and the Throttle Position changes.
Loose Vacuum Tree:If the Vacuum Tree needs tightening, be aware that these are a Gas Thread (meaning tapered) so tighten by Hand initially, then one more Turn with a Spanner is all that's necessary. Using Thread Tape can help the Tree seal completely.Overtightening may crack the Inlet Manifold. By BIJ 27/01/12@19:16 Shed
Trimatic Modulator Vacuum Source:
If the Car has a Trimatic, this is a good time to inspect and clean out the Vacuum Tree. The Tree can become blocked and cause the Trimatic to shift erraticly due to loss of Vacuum.