up and down

[gizmo]

the other day i notice that the RMP gauge is jumping like crazy. vehicle runs fine. I also opened the hood panel and it's sound like a vaccum leak.. any thought on the problem..... 1996 discovery SD

 

[NHESS81]

...my tachometer went crazy before the alternator died....might be your issue...what would a vacuum leak sound like? my alt. sounded like a fan was hitting a housing when it was dying...

 

[joey]

either alternater going bad, or the wire to the back is loose.