You can try something to help loosen the carbon and may save you some cash.
1. What you do is get the engine nice & hot.
2. Take the vent pipe off near the turbo intake.
3. Spray water into the intake where the vent pipe usually connects, not to much, just use an atomiser or something that restricts the amount going in. You may need a friend to assist keeping the engine revs up. Do this for about 15 mins, using about a litre of water.
4. Put the vent pipe back on & take the car for a spin & give it an Italian service.
5. Repeat step 2-3
6. Take the car for another spin & see if it has helped.
There is lots of info about water de-coke on the internet.
I have heard 50/50 reviews on water de-coke, half where professionals know what they are doing and get a good job done very carefully, the other half where people ruin the engine from doing it wrong.
Personally I just use BG 44K and if the exhaust turns black with carbon then you know there is a build up and you can repeat the use of this after 5k miles if it is was, you should notice improved when using the first application.
There is always the worry that you may dislodge a large chunk of carbon so you want to use something that will break it down good.
I have used it at every 10k, usually when I start to notice the odd misfire and then boom everything back to normal once I clean the exhaust back to shiny
Thank you all but its been sorted although I nearly had heart attack when I was told the engine needed de coking and they wanted 1300 pounds. But luckily the nice ppl at BMW agreed to make a good will gesture and cover the costs. One happy mum and relieved daughter
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