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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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my2006 focus sport labours briefly in 4th gear,also i have

Resolved Question:

my2006 focus sport labours briefly in 4th gear,also i have to do at least 20 mph in 3rd gear otherwise it does the same,but no problems if i do over 35 mph,also my tickover is erratic also,could you suggest anything.I would be very grateful.Also tried fuel injector cleaner in several tanks of fuel,using BP petrol as recommended by Ford

Submitted: 2 years ago.
Category: Car
Expert:  Shantal-Mod replied 2 years ago.
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Expert:  Matt replied 2 years 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 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
Might also be worth cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.
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
Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.
This leads them to be quite intermittent in the case of mild leaks
its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue
On no account touch the sensor wires with anything physical as they are extremely fragile
Customer: replied 2 years ago.

Thank you for your help,I cant here any hissing when the engine is running,but I shall take the car to a garage and tell them what you think the problem is,I was also wondering what the idle speed should be,mine settles at 750rpm,once again THANK YOU.

Expert:  Matt replied 2 years ago.

the idle speed should be a steady 700 to 1200 rpm depending on how warm the engine is

and yes feel free to pass on the suggestions
Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 20396
Experience: BEng hons Mech engineering, in auto industry 22 years
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