Dear jw144,

Hope you're well. The temperature gauge sender is found on the driver' side of the head (North American models), under the intake manifold, towards the front of the head (nearest the radiator). If you can fit your hand under the intake manifold, remove the plastic wiring harness connector (press the wire "bail" towards the connector's body). Use a wrench to remove the failed sensor. Do not worry about coolant loss: only a few drops will be spilled. Very rarely do temperature gauges fail: I cannot recall a post reporting such a failure.

The engine's rough idle could be due to a dirty idle air control valve. This unit is located on a bracket, below the intake manifold. It has two 1" diameter rubber hoses connecting to it. See the site's FAQs for instructions on cleaning the idle air valve. Be sure to keep the valve's nose - the end where the hoses connect - pointed downwards, to keep solvent from entering the motor compartment.

If the engine "dies" when warm, it likely is the ignition power stage. See posts of today's date (http://www.brickboard.com/RWD/volvo/1574799/940/960/980/V90/S90/93_940t_stalls_hot.html ), for how to locate and replace that unit.

Hope this helps.

Yours faithfully,

Spook