General rough idle when cold

[FASTMOGGY]

Hi all, 'Marmites back! ( the panda!!)
She's been running faultlessly since the crankshaft sensor incident But that annoying 'wobble' when she's started up from cold has re emerged, not all the time but your waiting for it every time you start up.
Also that' bad egg' smell has made a re appearance which happens when it's raining of all things so maybe the cat is cooling off a bit?
As for performance, She runs very well and giving me 55MPG average on modestly short runs of around 8-10 miles, pics attached.
In the past I have had the spark plugs changed to better ones as recommended here and new Ht leads which cured the problem last time.
The only thing I have done is to put 97% octane which really made her perform:slayer:
The bad egg smell and the 'wobble' have only re emerged since I put the lower octane back in, so could this be what's causing the issue?

 

[Goudrons]

Engine stumbles, rough idle and rotten egg smells from the exhaust/cat suggest it may be running too rich, though your mpg appears to suggest otherwise, it's very good.

I doubt it's due to 95 octane as the motor is designed to run on it.

As it's suffering soon after start up, it would suggest something is happening (or isn't happening) when it moves from cold to warm running (open loop fueling to closed loop fueling).
Perhaps there's a problem with the precat O2 sensor, like the heater element is starting to fail or it's a bit slow.

Does it run fine if you restart the engine when it's hot?

You could just try swapping the O2 sensors over, I believe the pre and post cat ones are the same.
The pre cat O2 control the fueling when the engine is warm, the post cat one just monitors the cats performance, so doesn't really need to self heat quickly.

 

[FASTMOGGY]

Hi, Yes she runs fine when warmed up and restarted , just the odd initial cold starts but I have to bear in mind winters on it's way so could be a more common occurrence!
My normal commute to work is only 2.5 miles so I have to do a slight detour so the engine can get up to temperature. Just out of interest, how much are the o2 sensors?

 

[Goudrons]

Genuine Fiat ones are about £150 +Vat or so.

In the past I've used NTK (NGK) without problems and they tend to cost around half genuine.

What out for cheap generic ones, you have to wire them in yourself.

The old ones can be a fecker to get out, I bought a cheap split socket type tool and it just slipped off and knackered the hex, so ended up with one of these.
https://www.machinemart.co.uk/p/22m...MI7Pb4tLy91QIVx6ntCh11iARjEAQYBCABEgLje_D_BwE

 

[koalar]

I wouldn't be over concerned about the smell. The fact you have a slight misfire will be responsible for this.

Try putting your hand over the tailpipe and see if pressure builds up. A hole high up will mess the mixture up.


A picture of the spark plugs may help. The colour would show if its running rich and if the misfire is on one particular cylinder.


My gut feeling taking into account it improved when you changed the HT leads. Is it will be something around the coil pack. Take a look at the connectors and clean the outside of them.

 

[koalar]

Dam

Mines started to do this.

Not sure what's going on. Its not as bad as a regular misfire. You can't hear it at the back of the car like a misfire. However you can feel it inside the car. Car drives fine

After filling up its not as bad.


Its almost like its constantly changing its timing.


There was another thread on here about a week ago. Strange three of use have the same thing at the same time.


Or is it the original thread has made us listen for it.