Clunking when car accelerator is pressed + Heavy clutch

[AdamDavis]

Hi all,

I have a 2007 Toyota Yaris Hatchback 1.4 diesel with 196,000 miles on the clock.

I have had this car for 50,000 miles now but most of the time when I press the accelerator after changing gear or after releasing the accelerator fully and then pressing back down on the accelerator I can hear a clunk noise and the car jolts a little bit (although this is not that bad). It doesn't do it all the time, but does it for the majority. I'm thinking it is something to do with the throttle plate but wanted to know if anyone else has experienced this and what it could be?

Also my clutch is heavy to press in, so wondered if this is a characteristic of the diesel Yaris or if anyone knows of an issue causing this? Is there a clutch assistance spring on the pedal that may be past its use now or could I get a spring to help push the pedal down?

On a related or unrelated note, my brakes also make a squish sound when pressing the pedal initially. Does anybody else have this or could this be trapped air in the system?