[Mk2] [Turbo] Missfiring on idle...

[Neil_87]

All other problems sorted with the car now, even code 24 gone!! No codes on ecu and all seems ok apart from this dam missfire.

I have put on another distributor, coil pack, cap, rotor arm and leads and the problem remains the same.

I forgot to gap the plugs when i put them in the engine, but i dont think its that.

Also wghen i looked at the plugs today, one was very carboned up (number 1 plug) and 3,4 were white on the tips.

Sounds like 1 is running very rich and the others are lean (didn't look at 3 yet)

Timing is correctly set to 10 degrees. I'm really stuck i just want to drive its been so long now

[djpkins]

if your plugs are iridiums then they will be pre gapped...could be the lambda or the cold start sensor on the water elbow if you've a rev 1...2, airflow meter, throttle position sensor....I have a similar but intermittent prob and thses items are on my list of suspects.

[Mike N]

If you have swapped items from a known good source ie a perfectly running car and the problem persists. You really need to carry out a compression test. Which will give you a result.

If cylinder pessure is noticeably lower on one pot it will be either:

valve - seat burnt stuck open off the seat or bent.
piston land broken
headgasket blown / head overheated and warped.

And even more so because you have rectified every thing else.
The richness you have described on one plug may be oil fouling so therefore a piston land may have broken allowing oil through.

Hope that it is a head gasket or valve as the piston which will not be visable untill its removed will cost a lot more time and money to sort, but can still be sorted with the engine fitted if the bores are not damaged.

Regardless of the outcome a new headgasket will be needed, so buy a MLS so that never becomes the fault next time.

Let us know how you get on.