Planning the next
AO Silver Member
Join Date: May 2007
Location: United Kingdom
Assuming you have a phase 1 ( sounds like it ) the sensor you changed is actually a pulse generator that generates 16 pulses per turn and up to a couple of thousand RPM. If that has been changed it is unlikely to be the culprit. It can however be tested by using a metal file ( have a search here on the forum - the procedure has been detailed before ) to bypass the pulse generator.
Two other possibilities come to mind :
1. The fault is within the instrument. Either the stepper motor or its control circuitry may be at fault.
2. When my alternator failed, the first indication I had was the speedometer playing up as the car's battery voltage dropped ( the charge warning light did not illuminate ).
With the former you're probably looking at a replacement speedo. To dismiss the alternator as a cause, measure the battery voltage with the engine running. You should have 13 to 14 volts. Less than that would indicate the alternator has failed. If the speedo problem is intermittent, you'll probably need a passenger to note the voltage when the speedo is acting up. The cigarette lighter socket is a good source to use for measuring the voltage.