Right Finally After A Year A Topic About Fixing My Flat Spot, Any Input Appriciated,

[Sphinktar]

Right Guna try bullet point this as theres lots of info to fit in and i dont wanna bore you with a massive amount of text
if you read on you will understand why i am scared to put a new cat converter in before my MOT as i worry it will happen again

1.3 2000 X reg sr

the problems started when i had a garage take my centre pipe out of the standard exhaust system
was fine at first but then a 2 or 3 month later my engine management light came on
my car then developed a small flat spot which has got worse over time

then it failed its MOT test on emissions he said they were thru the roof

trying too fix the problem i had the cat taken out and looked at, it was totally melted and useless it got binned as the exhaust centre said it had been over fueled
ive since replaced the whole exhaust system with a powerflow system and is currently decat'd
the flat stop has never changed no matter what has been changed on the car

the flat spot is only when first touching the accelerator and the car feels very sluggish untill in high revs
the only way to pull away is to tap the pedal till the revs build up


now for my MOT i have to put a cat back in and am looking to put an envy sports cat in but i dont want to put this in untill the problem is fixed
as if it breaks the cat again im £300 out of pocket

i heard of a simalar problem on an avensis where the first lambda sensor had broke meaning the ECU wasnt gettin the required information
wondered if this could have happened due to the centre pipe being removed and cause the engine to overfuel and ruin the cat?

any input is much appriciated cause i really wanna get rid of this once and for all

had the lamdors out the other day but was no good as you cant tell if there broke from looking at them there just pretty black

if it is overfueling how much am i looking at for toyota to put it right?
if theres anymore info needed jst ask ill get it edited ASAP
thanks in advance alex