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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22750
Experience:  BEng hons Mech engineering, in auto industry 22 years
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HiI have a ford focus 2001 1.6 zetec.I have a judder or

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Hi I have a ford focus 2001 1.6 zetec. I have a judder or misfire between 1500 and 2250 rpm "on light acceleration and deceleration" that seems to get worse when the weather is colder or damp or both. It also idles slightly irraticly. when you start it from cold it does always start but as soon as it fires the revs go up to about 2000 then drop off to about 750 then it picks up again as it should do. I have done a service. plugs, ingnition coil, ht leads, oil, oil filter, fuel filter i have changed the idle control valve "which seemed to make it worse" i have fitted a new cam belt and tensioner and i have fitted new breather hoses "the t peice bit under the inlet manifold" because on of them was collapsing under load. i even brought a second hand map sensor but nothing seems to work. im going mad please tell me u know what the problem is. There are no codes on the ecu by the way.

I have also had the pcm updated at a ford main dealer.


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 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.

my car doesnt have an airflow meter.


its also called the MAF meter and is located just after the air filter box

looks like this


and is located here
Customer: replied 2 years ago.

Hello. My focus doesnt have one. Some focuses do and some dont,

Mine doesn't.

anyway, there is an air sucking noise and its coming from the join of the fuel line to the regulator ? It must be a bad join causing low pressure.


OK I'd tackle the 'sucking noise' which is air being drawn into the engine - if its just hte small diameter ose that plugs into the top of the regualtor then try cutting the hose back by 1cm or so to provide a fresher bit of hose and then re fit it

If this doesn't help then I'd next suggest measuring fuel pressure with a running engine
Customer: replied 2 years ago.

Its coming out of the main return pipe thats attached to thd bottom of the reg. Im going to have to buy a new pipe as its the o ring on thd clip thats worn out, unless u have some fix I cant think of


you can get o-rings seperatly

I don't have teh exact size to hand but if you have the old item then I'd suggest finding a local bearing / industrial supplier and they should be able to match it up for you

if you can let me know your whereabouts I'll try and suggest a supplier
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