98 freelander derv idle problem?

HELP NEEDED i have a 1998 freelander just bought 2 weeks ago problem i have is as im driveing it purges forward {like iits going to cut out } and when you stop it tick over is normal then it goes up to 2500 rpm to 3000 rpm then back to 2000 rpm for no reson i have noticed that the temp gage dosnt work and not sure if the fan works could this be the proplem any help out there please have been told that it might be the new cluctch please help