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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20396
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 2006 V70 D5 est 185bhp 2014k miles good engine no

Resolved Question:

Hi,i have a 2006 V70 D5 est 185bhp 2014k miles good engine no smoke etc
For some time now i have experienced a flat spot on the throttle very low down in the engine revs/hardly any throttle depression that can be driven through but is getting worse, on my daily commute is no real problem but have recently been on holiday in the car driving in a very hilly/mountainous region & it is much more of a problem, also have experienced problems in meandering traffic at low-ish speeds & when i come off the throttle completely as when rolling down a long hill it sometimes feels like the brakes are applied or engine is switched off, i have been concerned that it may break down but never has,as i believe this car has a "fly by wire throttle" & i seem to be able to pin-point the dead spot with my foot while driving could it be a problem with the sender at the pedal & is it a big job to replace. ps the car is due its service & will be going into main dealer for this next month.
Submitted: 1 month ago.
Category: Car
Expert:  Shantal-Mod replied 1 month ago.
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Customer: replied 1 month ago.
Hi i will carry on waiting for an answer to my question
Expert:  Matt replied 1 month ago.


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 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

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

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

Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20396
Experience: BEng hons Mech engineering, in auto industry 22 years
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