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Matt, Mechanical Engineer
Category: Audi
Satisfied Customers: 22927
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I just bought a 2006 20lt tdi automatic New turbo was fitted

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Hello I just bought a 2006 20lt tdi automatic New turbo was fitted but I have noticed a very slight drop in the idle ever so slight when it is sitting ticking over it almost feels lump like dirt in the diesel but drives perfect can you advise me please. Cheers


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

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.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

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.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

It’s also worth cleaning the MAF sensor wires, as they can get coated with dirt over time which then offsets the reading

Use some contact cleaner or brake cleaner to spray onto the wires to remove the dirt – on no account touch the wires with anything as they are very fragile

Customer: replied 1 year ago.
Thank you Matt I am just really worried it was something to do with the gearbox. Because I heard all sorts of stories about the flywheel being done. I did notice after a drive today when I arrived home and stopped on the drive and putting the car into neutral it started and into park it stopped So I will get it looked at sometime soon.

well if you're worried about the dual mass flywheel being worn out then this will show up if the gear lever is vibrating a lot

Customer: replied 1 year ago.
No vibration in the gear lever at all just a slight drop when it is ticking over I forgot to say yesterday I noticed it more when I tried to put the aircon on To me it felt as if the load was being put on the altinator to kick the AC on and the needle in the revcounter dropped. Like I was saying lumpy on it. So I started reading on google and that's where I heard about the flywheel. Thank you for your time and help. Think the way I am going to go is try the first option you said to do and look for airleaks


best of luck

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