I have a 96 XJ with an annoying problem related to the instruments.

2 out of 3 times when I start it up it will send the tach needle to about 2200 RPM and stay there during idling (engine is running at 1000 RPM or so). If I give it some gas the needle only moves slightly north and then sinks back to 2200.

After about 20-30 mins the needle will drop and the tach will read semi normal (idles at about 1100 accoring to tach, would say its a bit lower IRL)

I have tried to clean all connections leading up to the computer as well as the connections at the cam sensor. Crank sensor is new.

Could I somehow re-route the tach wiring to read from the alternator or what could solve this? Could it be a mechanical fault behind the dash?

 

Nobody?

 

My tach and gauges were twitching so I tried to pull the needle out and put it back in...turned out to not be the problem. After I did this my rpm gauge acted like you described.
Clusters are usually around $20-$40 at junkyards so you may have to try a different one to find out.
When my gauges were twitching and quitting my 2nd thought was that the ground was bad. I ran a ground screw from one of the GND labeled screws on the back and this fixed my gauges and made the backlights brighter.
It's very hard to guess what the problem would be in your case so that is why no one wants to respond.

And I am referring to my 94 cluster fyi.

 

Did you fix your tach issue?

 

Hi, sorry for not getting back.

I tried with the extra ground and cleaned all the connections I could reach, both under the dash as well as the ones under the hood.

I think I'll take the dash apart, I have two bulbs that have gone out as well, so maybe I can fix it when in there.