Just was thinking about this one and had some idea's that haven't been mentioned.
Have you checked for any DTC's that the ecu may have thrown or stored? There could be something. When I replaced my coolant temp sensor a while back my problems came back a couple days later. It turned out to be some "flakey" wiring/connector. The DTC was cleared with my logger, non active, but was still stored in the ecu. I had to reset the ecu to fix the problem after rewiring the sensor harness because the logger would not clear the stored code.
Also, IIRC the speed sensor increases idle when activated. So if your cruising and check the idle speed it should be higher than normal. This is to add vacuum to assist with braking.
