First, I'm new to the forum. I own a 98 es300.
I've had this problem for a while but it would usually go away, but it's stuck with me for a long drive today. My speedometer and odometer are not working. They are still illuminated, but the needle doesn't move and the odometer is blank. When it was anot uncommon thing, I noticed it mostly happened during the summer when the car was hot. It messes with the cruise control as well. I haven't noticed any problems with driving the car, however. It still runs and drives smoothly to my knowledge. Any reply is appreciated.

I'd like to know how fast I'm going.

edit: literally just watched the needle spasm up and down and the odometer flash on and off. I was going 80 on a highway

 

Hm, had this problem on my '99 Cavalier back in the day (laugh it up, fuzzball). Turned out to be speed sensor. 'Course, the rest of the cluster would spaz out sometimes but that was typical GM "quality"...

EDIT: output speed sensor is the primary culprit. Also check codes.

 

Blank odometer would make me lean towards a bad speedometer assembly. NOT the entire instrument cluster, but the section that includes the odo and speedo.

Use speedkar's guide if you would like to replace it yourself.
(Pop off the trim, unscrew the instrument cluster, take off the smoked plastic, remove the MANY screws, take off the black face, unscrew the speedometer.)

You can probably buy an entire instrument cluster for $25 at your local junkyard.

Mind you, throwing in a used odo/speedo WILL mean you'll see a different mileage.
You can use the same guide to reprogram the odometer or make note and live with the altered mileage.