1st gen. Yaris idles rough and shuts itself off

[pastatore]

Hi!

Here to ask for suggestions.

I have a 2002 Yaris with the 1.0 1SZ-FE petrol engine. Lately the car has been shutting itself off, the engine idles pretty rough and there is a lack of power when in 1st gear. Hill starts have become a nightmare. The car also has trouble starting but alternator, Battery and starter motor have been tested and proved to be fine.
The issues I've described get worse when the car is hot, after driving it for more than 40 minutes, it is practically unusable, continuously shutting itself off.

Engine management light is on, suggesting a fault with the oxygen sensor located on the catalytic converter.

Could it be a clogged cat or might the issue be related to the throttle body? I’ve heard people in the past having this issue and it being due to the throttle body malfunctioning.
Can't visit a mechanic at the moment due to a lack of money.

Thanks in advance, wish you all a nice day

[Madasafish]

Things to check at no cost:

Air filter not dirty

MAF?MAP sensor wire dirty? Clean with carburettor cleaner.

Get codes read by someone with a code reader.. That will pinpoint area: 

Lots of potential areas.. costing ££s

[pastatore]

4 minutes ago, Madasafish said:

Things to check at no cost:

Air filter not dirty

MAF?MAP sensor wire dirty? Clean with carburettor cleaner.

Get codes read by someone with a code reader.. That will pinpoint area: 

Lots of potential areas.. costing ££s

Air filter was changed today together with oil and pollen filter. 
I can give a shot cleaning MAF/MAP sensors and wires, do you happen to know exactly where they’re located?
Codes were read by two different mechanics, both said they are related to the oxygen sensor on the cat but said values of the sensor are within manufacturer spec, suggesting that the sensor works ok.

[flash22]

if you snap the throttle does the engine fall flat on its face.

pull the plugs and inspect them, if you're unsure post a pic of them

[pastatore]

2 minutes ago, flash22 said:

if you snap the throttle does the engine fall flat on its face.

pull the plugs and inspect them, if you unsure pust a pic of them

When hitting the throttle the RPMs briefly lower and then rise again after considerable vibration. Forgot to mention plugs were changed today together with the oil and filters

[flash22]

check the resistance of the OCV

 

[pastatore]

1 minute ago, flash22 said:

check the resistance of the OCV

 

I’ll try that, thanks. Could a loose timing chain be causing these issues?

[flash22]

OCV 6.9 - 7.9 ohms is the range iirc, it may vary with temperature - below 1 ohm is a short circuit over 10k ohm is open

[pastatore]

6 hours ago, flash22 said:

OCV 6.9 - 7.9 ohms is the range iirc, it may vary with temperature - below 1 ohm is a short circuit over 10k ohm is open

Resistance is fine, cleaned the OCV and it's made no difference. I'm starting to think the chain is rattling a bit, maybe it's gotten loose and it's causing these issues, who knows. 
I'm not too sure though, it is noisey but does not sound noisy enough to be cause of worry.
I'm at a loss. Ordered another throttle body, let's see if that can solve the issue. I'm just preying the cat is fine since they are hard and expensive to get

[flash22]

do a vacuum test, start the car, and spray a bit of carb cleaner/brake clean around the intake manifold where it meets the head, especially around 3 and 4

age and heat cycling makes the o-ring gasket shrink and go hard, this would also explain the hot and not running issues and o2 codes as it would run lean, the ECU will just make the engine over fuel

if so replace the gasket with a good quality item like a Victor Reinz 71-53109-00

if the chain or tensioner was at fault you would hear it from cold, you will also have cam and crank codes and even correlation codes