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I'd first check all the high pressure hoses post turbo/s for any split hoses or cracked metal pipes, also check the ends of the intercooler as its not unheard of to pop the end caps off under high boost.
If this is OK then check the small vacuum lines to the turbo and its connected control solenoid on the bulkhead, any cracks or leaks can give turbo issues and its best to have the boost pressure measured actually measured with a boost gauge to check that the turbo is healthy and that the sensor is reading correctly
Also have a feel around with your bare hands with the engine running to see if you can feel any escaping gas under your touch. Another method is to use a soap and water solution sprayed onto any suspect areas - if there's a leak it'll bubble up with the engine running
If this is OK then remove the high pressure intake hose after the turbo and have a feel of the turbine wheel - there should be no play radially at all - but a little bit of axial / end to end float is normal
If this is OK then check for air leaks after the mass airflow meter - The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Would you say its the Boost Pressure sensor or more likely to be a split pipe, also where is the turbo located as I cant see it from the front, I can see the EGR valve so would i have to get at some of the pipes from underneath removing belly first?
When I accelerate hard everything is ok, the fault has only occured when I have hardly any accelerator on and virtually coasting, last night on the drive I revved the engine hard and then all of a sudden it would rev no more, any ideas on this one or part of the same fault?
Thanks for the help, the garage I took it to said the wast gate was sticking, can this be changed seperately or is it part of the complete turbo, another thing they picked up on was battery voltage low, the car always starts first time but i have had the battery light come on a coulpe of times, I am getting a new battery but could low battery voltage cause the issue of limp mode if the signal is incorrect? Also on the top towards the front of the engine there is a flap valve with 2 sensors on, what is this valve?
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what does this flap valve do as there are a couple of sensors on it, i think th emain problem is the EGR valve so will remove and clean this week, what are your thoughts on blanking plate or restricting plate for EGR valve, car has done 101K, I have no Engine Management lights come on when fault occurs and everyone recommends cleaning the EGE Valve out and blanking off but this will result in fault within the engine system, how easy it is to get someone to reprogram software to ignore EGR valve? Also where is the boost pressure sensor located, i am an engineer and carry out my own services so am willing to try anything.