Rough Running, Misfire on Idle, Stinking CAT Convertor

[Integrale1]

I recently parked my 172 phase 2 up for a couple of weeks whilst I was away with work. Driving it home on my return I noticed it had a bit of a hesitation and surge when applying a small throttle movement at low rpm, (i.e. accelerating at 40mph in 5th gear). It also felt like it had developed a slight misfire. I presumed this was through lack of use and the weather being damp and freezing.
Next day it started fine, ran ok when cold then ran rough once warm. It started to misfire when revved in neutral and stationary, you could hear it pop and bang through the exhaust. The CAT had started to absolutely stink of a sulphur smell.
It seems worst when warm and at low rpm, under load or idling.
I took it to my local Renault specialist and they plugged into live data and noticed the pre CAT lambda was sticking at either a high value or a low value, it apparently is mean to flow between these two values, not stick at them. So the lambda was changed and it did drive better for about 20 miles and now it's back to its awful running.
Today I changed the spark plugs, leads and coil. All the old spark plugs were fine apart from cylinder four, it was almost burnt to a cinder on the end.
I've checked all the wiring, it's had a new crank sensor (with the modified loom/pins)
New Spark plugs
New Coil
New pre CAT lambda sensor
New ignition leads.
And it's still as bad as ever.
It's flagged up the flashing engine management ight but this goes off really quickly and when plugged in it had no fault/error codes on it?

I know rough running issues with these cars are ten a penny on here but I've looked through them and can't really find out what's wrong with the car.
So, does anyone have any idea what the fault could be?
Appreciate any help

Dan

 

[Ol’ Tarby]

Dodgy injector on cylinder 4 maybe?

 

[Dan.AS]

This ^^^

 

[Integrale1]

Would a dodgy injector not throw up a fault code or anything like that?

 

[charltjr]

It depends. The misfire fault codes can get cleared by the car once the misfire stops. Given what you've replaced so far and the symptoms my money would be on a bad injector too.

Just replaced one of mine, there's a guide on here and it's DIY-able with some patience and guts.

 

[Integrale1]

Excellent, thank you guys for your feedback, I'll change it tomorrow and see how I get on.

 

[bloke]

flashing eml is an injector and it will store a code regardless of the light flashing or clearing. as long as you use something half decent you should be able to see a code for it.

 

[Integrale1]

Update,
Car is fixed, it was the cylinder four injector, runs better the ever.
Thanks everyone for your help.

Dan