Ok so I've been told I need a new left side catalytic converter.
Great.

I had a p0420 code and a P0102 code.

The garage said both of these could be caused by the broken cat. I'm not convinced on the p0102 code?????

Also how do I diagnose and repair the p0102?

 

Well you could swap the O2 sensor from side to side to see if the code changes? Might just be easier to remove the cat and take a look.
.
.
.

 

+1 on removing the offending converter from the exhaust and inspecting thoroughly - if I recall correctly you did have misfiring issues, correct? Unfortunately, misfiring coils (if not rectified quickly) can send a cat converter south very quickly.

 

yeah did have lots of misfiring issues, and also had the timing chain jump one tooth so the timing was out as well.

how can i no for sure if the cats dead?

i dont really have the time or space to take the cat off the car, its snowing in the uk as well lol.

i have a code reader which does live data so i can read the o2 sensors, but dont know what im looking for?

 

Er, P0102 is a problem with the MAP. PCM uses it to help it get fuelling right.
edit: Sorry!!! It is MAF. grr. Dunno what I was doing.

Your car is the older type (pre 2002.5MY / 2003MY USA), so all 4 O2s are the same type.

Both upstreams should switch fairly often from high to low and back. STFTs should wiggle to cause it. Both downstreams should hardly move and do it less often. The banks should be very similar.

You need them HOT to have them happy so idling isn't really ideal. Rev for a minute or two and watch. I think they'll go on switching if you let it go back to idle but may largely stop as they cool. Cats don't do much unless HOT also, especially old ones.

Think ugly sine wave if you want an image.

I hope a tech will chime in if I've got this misleading as the last time I had a car with these older type O2s was some years back!