If you have a Mk6 van that the speedo needle "jumps" from 0 to 10 Mph when idling, or the fuel guage / temp guage wobbles for a few seconds after starting, or any of the guages take a while to respond even when driving (sometimes odd warning lights can flicker on and off too), its is usually due to one of the following.
Either the multiplug connections on the back of the instrument cluster are making bad contact, and should be removed, sprayed with good contact cleaner then pushed on and off several times to "clean" the pins...or if that fails to resolve the issue...
Your charging voltage has become unstable (usually more noticeable just after starting), and is 9 times out of 10 due to a failing battery (regardless of what charging voltage is when checked with a multimeter) These vans require a steady voltage for the electronic guages to work correctly, and any variation can cause strange effects with the instrument cluster and sometimes the radio! .......
As a last resort your alternator should be checked, but only if the above dosent solve the problem.