speedo/rpm jumps up/glitches

[Mxcy]

so i have this problem with my mk1 phase 2 2004 1.0l yaris (scp10 french built)

when i am driving, the rev counter will sometimes jump around, so i will be driving at 3k revs and all of a sudden the rev counter jumps straight to 7k for a split second then back down, the engine doesn't actually rev, its just the counter, i have the same issue with the speedometer, going about 65mph and the speedo is jumping 60/65/70/75 just jumps to random numbers, so its very difficult to tell how fast you are actually going, i know for a fact that im not going 75 when i was going 60mph 0.1 seconds before and am using the same revs, if anyone could help me out here then i would be so happy, as its very difficult to monitor speed etc and annoying too, i will record a video of the speedo and me driving normally to try and show the issue better at a later stage, 

 

any ideas? mot is coming up next month and wont pass without a working speedometer!!

[FROSTYBALLS]

Have you tried disconnecting the Battery for a few minutes to act as a reset?

[Mxcy]

1 minute ago, FROSTYBALLS said:

Have you tried disconnecting the battery for a few minutes to act as a reset?

disconnected Battery overnight and still does it :(

[Mxcy]

ripped the gearbox bolts out last night, so going to have to get a new gearbox aswell now, looks like this car may just be worth scraping

 

gearbox repaired, still need a fix for the speedo, going to try unplug the Battery for a few hours again