Loss of Power When Warm

Hi, first post here and would appreciate some good knowledge.

Have had the 197 for nearly 6 years and the flexible part of manifold started to go.
So being an expensive repair I decided to go to an independent RS garage.
Not so easy to find in the land of clogs and don't speak Dutch! :kilt:
RS independent garage fabricated a manifold without pre-cat and cat from RS 200 through to standard exhaust. It sounds great, was not looking for any performance gains but it did seem to feel that an extra horse or 2 had been unleashed. I was very happy......

However, after a few days, a problem occurred after the car is warm there is sporadic loss of power. No revs when I press the accelerator, just backfiring and the smell of unburnt fuel is intoxicating!
So the car went back to the RS "specialist" and they changed spark plugs and cleaned the throttle body, no fault codes. Yeah got the car back to Rotterdam but failed again when trying to park in the garage at home.

So It runs when you have momentum but when warm from stationary the problem starts.

I gave up on the "RS garage" as it was looking like a cash cow....:chris2:

I do think it could be dodgy O2 sensor on the manifold.

I have read a lot on different forums like this:
https://clio197.net/threads/lack-of-power.41568/

and:
https://www.cliosport.net/threads/rs-clio-197-f-d-after-exhaust-fix.811435/

They sound like similar problems but the posts do not mention the smell of unburnt fuel.

Can anyone give me some input to this problem?

It's one of those problems that could cost many euros to fix if left to a garage :money:

The car is worth fixing as I think it looks good for an old one :200T:View attachment 133550 View attachment 133551
 
no cats means less restriction on the exhaust so the fuelling is out & wrong needs a rolling road re-map
 
no cats means less restriction on the exhaust so the fuelling is out & wrong needs a rolling road re-map
I was aware that a full de-cat would require a re-map but it still has the main cat. Just getting rid of the pre-cat I thought would not require re-map?
 
Getting rid of any cat requires a remap really, though the pre-cat isnt as restrictive. The lamba is registering that the exhaust gases are different so possibly overfuelling.