Thermostat housing replaced now car is shaking and revving

I have just had my thermostat housing replaced as it was leaking coolant, since then when I start the car the dash and wheel shakes ridiculously sometimes it does not start and sometimes it is as though it stalls. Setting off to work this morning it struggled to get going and whilst I am still in traffic or parked up the car is revving by itself.

i had taken it to the garage this morning but it seemed to be fine whilst there, it is not as bad not it is as though it was a blip.

can anyone help?