I think this is the first time it's happened in the year+ that I have owned the car. The needle jumps at idle from 500 rpm to about 1000 rpm, the engine does not change idle speed. There is a click sound from the engine bay that I have wanted to diagnose; it sound almost like a relay opening and closing. it's a metallic sound.

No engine work has been done, just suspension. The Neutral Safety Switch was replaced recently, although with an aftermarket version but I may install the factory Volvo version.

What could cause the tach needle to jump?
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1991 745 & 1993 965 /// RIP: 86 764T; 79 262C

Dear ChrisS,

Hope you're well. Tachometers themselves do not seem to fail very often. To clean the instrument cluster contacts - on the harness and on the flexible circuit card - use a rectangular pink pencil eraser, of the sort with wedge-shaped ends.

Rub the eraser over the contacts a few times. Be sure sure to blow away any rubber shavings.

The eraser suffices to remove an oxide film, so thin - perhaps only a couple of atoms thick - that it may be invisible to the unaided eye. Removing that oxide film can restore a good connection.

On the 1995 and later 940/960 clusters, press down on the catch, to release the wiring harness connector from the cluster. Pinch the release catch between thumb and forefinger, and the connector will be released. No tools are needed to do this.

Hope this helps.

Yours faithfully,

Spook

Pull out the instrument panel. disconnect and connect all terminals. Mainly tighten the screws that hold the instruments dials.