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My plugs are clean,but white,indicative of a "lean" mixture.The car slows and then picks up,on the throttle,when cold,although this seems to disappear when the engine warms up. I've changed the plugs and leads to no avail.The engine management light is not coming on,tho' I've been told that a MAF sensor fault will not cause it to do so...?Any ideas...???? Lambda sensor problem or vacuum leak,perhaps..???
Can you get an error code?

I had a similar problem a couple of years ago with my car 'running lean' I cant remember the code at the moment, sorry, but it turned out that just behind the exhaust manifold, theres an 'E' shaped air tube, one of my tubes had split making the car run lean, my mechanic did a quick repair with some insulating tape, no more light coming on, and the next time he serviced my car, he fitted a replacement part for me, a little warning, its a bugger to fit, you may have to take the manifold off.

hope this helps
The error code I was getting was P0171

Hope this helps
Thanks for the info.I've not ,as yet,plugged in a code reader so don't have a number.The fault appears to be intermittent as it didn't happen for a few days, but did a couple of times tonight....Aaaaaarrrrggh!
Hi all, I am new here and I try to find solution for my Ford Focus Turnier, 1,6 petrol engine. Car is from 2009 and has app. 45k km. So not so much. One year ago an orange engine led came on. Serviceman made a diagnostics and it came a P0171 out of computer. He just made a reset of it. 3/4 year later after 10k km, orange led came again on, with same error code and I was advised that front O2 sensor is damaged. Ford dealer here in Slovakia, demanded over 300 Euro for replacement :angry: . So I tried to contact another car service, where was Air filter replaced, sparks, MAP sensor and fuel pump cleaned. No leaks on air hoses were found. Injector cleaner was also applied. After 700 km , led is again here. Did someone form you already found a solution for this? I read few hints on internet, in more that 80 % of cases it is a leak on any of hoses in car. rest is a dirty MAF/MAP sensor. In some case was also O2 sensor changed but problem remained. Car is running quite, well also on motorways or highway. The only one problem what appear after the led is on, is a bad starting ( warm and cold engine) Car is lazy to start on first time, i need to press more times on gas. What I found on various car web pages, that there can be also problem with PCV hose - positive crankcase valve hose, that there can be a problem. Can you please advise where this hose is located in car? I think this should be somewhere in the bottom part of engine. Thank you Roman
PS;what i forgot to mention, car has a average fuel consumption at 8,3 -8,5 lit. /100km. and idle is running also quite well with minimal oscillation, but when I open the hood and look at the engine, it is shaking a little bit irregular. Oil was changed app 15k km ago -Formula F 5W-30. So I would appreciate any help from you. Thanks
I have this on mine now :(
hi Jason, my car is back from mechanics, they told that the cause for my P0171 - running lean error, was dirty PCV valve - positive crankcase ventilation. In comparison before PCV was cleaned , starts my car better.Also idle is better .I will check the car now while running. I hope that problem will be solved now, but still I am still a little bit skeptic. :unsure:
hmmm, the led is back :angry: :angry: :angry: i will try to buy a new PCV valve, seem that the spring is weak. part should cost app. 20 euros, part number should be 6A666 not very neat number :angry:
when you do the valve its best to do the hose as well they commonly collapse
PCV valve gives a rattle sound.but no idea how looks the spring inside.if it is in good shape or not.need to check with dealer.when i breath through it,air is flowing through it in both idea if it is normal :-((

for the price the only way to be sure is replace it when they go they go the spring weakens easily think how many times a day its compressed
Hi, I am back again. Car was 4 days in repair again. Diagnose = defect front O2 sensor, part replaced, 300 km runs car fine. I hope that this is already final diagnosis :-)
I`m back again, 1200 km was car ok after front O2 replacement and orange engine diag. led was off. I was on holiday driving the car for 400 km, stopped for a while app 30 minutes. Started again run app. 4 km and engine led went on with a strange noise 'cssss" exhaust maybe.
So I enjoyed my holiday and drove again app. 150 km with engine led on, stopped for dinner, started car again and .......
engine led is away, but what remains is problematic cold start. Car wont start on first time without pressing gas pedal.
I start to think that there is something leaking near exhaust. Any suggestions please?
so car is still in service with another diagnosis - bad fuel pump. It gives only 2.2 ba pressure, instead of 3,9 as the mechanic said. No idea how pressure should be. Fuel pump cost 450 Euros, cool, car is worth maybe 8000 Euro. it is a piece of crap :-(
i take it you dont have a ford dealer take it there if you do and get a proper opinion before you commit if the fuel pressure was low i dont understand why the car drove fine as you go faster the pressure drop should cause the car to kangaroo as theres fuel starvation

i have the same problem and i'm now lost . i've fitted



oxy sensor


inlet manifold gasgets

fuel filter




thottle body

coil pack


air temp

crank case breather

all from my dads fiesta mk4 running fine           non of this helped


today fitted  injector rail complete   from scrap yard



all pipes seem fine can't see any leaks 

misses when cold then lack of power under load

inlet manifold seemed to be dirty with oil    ?

have ordered   new crank case breather valve for tomorrow 


code still  coming up p0171  


any help please i'm now demented    only bought car last week wish i hadn't now .

P0171 is either a faulty or dirty maf a vacume leak near the maf a faulty pcv valve dirty or cligged fuel filter or the 1st 02 sensors faulty there are two so its either a vacume leak or a faulty pcv valve

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