Madasafish

It is a 16 year old car... The suspension is likely to be worn. The brakes will be past their best. Do you have tyres from a reputable make or cheap budget ones on..? If cheapies, then spend your money on them. I would not bother: the extra power could be the last straw for the engine..

ALWAYS FIRST check the drains under the front winscreen wipers at the rear of the bonnet.. and clear out dead leaves etc..

It sounds as if you may have a damp problem. When car warms up, damp disappears. I would check under the bonnet drains are not blocked.

Picture would help

https://www.toyota.com/owners/resources/warranty-owners-manuals/yaris/2004 2004 one (should be very similar) https://www.manualslib.com/manual/837225/Toyota-2000-Yaris.html 2000 model

I fitted mine just under the rear view mirror on the passenger half. You can see it easily by glancing up at the mirror.. and from the outside of the car it does not stand out.. (I ran the wires along the front shelf, up under the trim of the driver's A post, under the edge of the headlining and down just after the mirror.. so minimal wiring seen.)

I go slowly through floods . You may not know how deep they are and if the water reaches the centres of the wheels, the engine belts will become wet, and spray water over everything.. - and possibly slip.(been there last year in our Jazz: lower radiator aperture covered in leaves.. Cars are NOT watertight and water entry through the floor can do serious damage to cars where the makers place key electronics (Audi).. Some of our local lanes have a stream at the bottom which floods.. and you can have no idea of the depth.. Rather safe than stuck in water..(seen that too) . and dry out brakes afterwards as they will be wet and will not work properly.. (seen the results of that too)

" the engine suddenly started cutting out as I was driving it. The airbag symbol would appear on the dash first for a few seconds and then the other dash lights would follow" The sudden cut out suggests an electrical problem. (Fuel starvation would give hiccups). First start by checking all earth leads from battery to engine and to body .Remove, clean up, replace. Ditto battery terminals.. Then wait and see what happens..

I have a front dash cam fitted via cigarette socket for 7 years. No problems at all....I use a two way splitter to power my satnav as well if I use both together..

Interference from a strong source..microwaves?

Do you do short journeys most of the time? It may just need running at higher revs to clean out the crud caused by stop/starts at low speed when cold...

You cannot just change the clutch. The gearbox needs specialist resetting.. after a clutch change.. DO NOT take it to any garage: it requires a specialist in the MMT gearbox to sort it. Even Toyota dealers are ignorant of it.. It is unlikley there is any specialist knowledge of it on this forum as it was notoriously difficult to solve faults and the advice is not to buy ..

EGR valve may be blocked or dirty MAF sensor or dirty air filter or plugs failing/wrong gaps or failing ignition coil(s) If no fault codes the above apply. If any warning lights, read fault codes.

You did not mention the mileage. If it has done few miles - less than 10k a year - and used only on short runs, it may be all carbonned up and the catalyst and dpf may be partially blocked... Try an Italian tune up.. at least 30miles with rpm exceeding 3,000 flat out rpm is better at all times. This will heat up the engine and could help clear it out..

If worried, a small battery device plugs into the lighter socket and will stop data loss.