182 Misfire/Low RPM Stutter

[whereislee]

Hi All,

About a week ago now I've noticed the Clio's developed a low RPM stutter and throwing a P0300 random misfire code (flashing EL).

Parts replaced in the last 12 months:
- 12 months ago: 4x brand new Magneti Marelli injectors
- 600 miles ago:
- 4x NGK R spark plugs
- air filter

Symptoms:
- stutter below 2000rpm in every gear, pulls hard and runs perfectly fine above this
- no additional fuel consumption
- I did remove the intake manifold/plenum and recheck all the connections/leads to the coil pack + spark plugs and it ran fine for a bit and started stuttering again.
- (not sure if symptom) exhaust is a little sooty so could be the precat LAMDA? pretty sure these are still the original LAMBDA (119.5K miles now)

Any ideas? Thanks!

 

[MRBILLYUK]

You've already changed the usual suspects. I'd change the pre cat lambda sensor for a genuine Bosch one. I think Bosch recommend that they be changed every 90k miles.

https://www.ebay.co.uk/itm/303441549650

 

[Bankrupt_drunk]

If the exhaust is a bit sooty and black then it might be worth getting it in an emissions machine to see what's up. As above I'd suspect the pre cat lambda failing and it's running a bit rich.

 

[whereislee]

thanks guys! will get a pre-cat lambda and give that a go.

 

[whereislee]

so swapped in a new bosch pre-cat lambda (did a major belt + dephaser service at the same time), drove very well for a while. The very slight stutter has come back. Thinking HT leads or coilpack? Any pointers would be appreciated!

 

[MRBILLYUK]

so swapped in a new bosch pre-cat lambda (did a major belt + dephaser service at the same time), drove very well for a while. The very slight stutter has come back. Thinking HT leads or coilpack? Any pointers would be appreciated!

I had a 172 years ago and it developed a stutter like yours. If I remember rightly it was up to about 2500 revs then above that it would be fine. It was the spark plugs. Changed them and it was fine after that.
So yeah "could" be HT leads or coilpack as you've already changed your plugs.

 

[Touring_Rob]

Mine had a similar issue, in the end it turned out to be one of the HT leads, but there was also signs that I had at somepoint got a load of water down plug holes so top of plugs were very canky.

New plugs and HT lead set and the car was back to normal.

 

[whereislee]

I bought new leads and installed them last Friday. The #4 magnecor HT lead had a nice 1.5-2cm split in the boot. Car seems to run much smoother now and feels like its making the power it should.