I can not solve the issue I'm having on my 2010 mk skoda octavia vrs. Engine code CCZA. When starting the car from cold I have a bad missfire and really rough idle where the car will cut out if I don't get it moving quickly.  Once the car is warm its fine. I have so far had spark plugs and ignition coils changed due to engine codes pointing at missfire in cylinder 3 and 4. This made no difference, there's no vacuum leaks pcv has been checked and is fine. I then thought it might be carbon build up on intake due to short journeys I make so had the inlet walnut shell blasted and all four injectors were changed but still no help. The only other thing I have noticed is an oil build up on top of the gear box but don't know if this is connected.  I am almost ready to give up and get rid of the car which is a shame as it only has 66000 miles on and has been looked after. Any help or advice would be really appreciated. 

Hello!

I'll just chip in with some other causes that could lead to misfire.

 

From what you have said about the PCV system working fine this is probably an unlikely cause. However, it is probably worth to check the rear main seal, this issue can cause misfire to occur when cold starting and even stall the engine due to the vacuum leak. This can also cause an oil build up between the engine and the transmission ( check if there's oil between the engine and the trans and not only on the top). However, as i stated it is probably an unlikely cause as your PCV is working fine and no vacuum leaks being detected. 

 

Another source of missfire can be that the engine is out of time. I dont know how long you have had this problem but a stretched timing chain due to bad tensioner (know problems with these engines) it could lead to misfire.

Do you have an updated tensioner? Probably good to have it checked. 

 

It could also be an engine coolant sensor going out due to the misfire being present only during cold starts. The car's computer having the wrong temp and having the fuel mixture too rich or too lean. 

 

A failing crank position sensor which can lead to misfire due to wrong signals being sent to the computer.

 

I know this is a lot, and may not be much use but these are just some other causes to misfire.

 

I hope that you can get the problem figure out as soon as possible and good luck!

 

 

 

Thanks for the reply , I did think the coolant temp sensor could be a symptom but was put off the idea from a couple of mechanics.  Do you know whereabouts this is located?

 

2 minutes ago, sykums said:

Thanks for the reply , I did think the coolant temp sensor could be a symptom but was put off the idea from a couple of mechanics.  Do you know whereabouts this is located?

 

 

Fast forward to about 1:50 and you'll find it.

It's in quite the tricky spot - german designed 

 

 

Have changed the coolant temp sensor and still no change. Anyone had similar issues?

my guess is carbon build up

@sykums, have you sorted it out or sold the car ?