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Is my lambda sensor to blame?


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#1 Thoric

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Posted 20 September 2009 - 10:19 PM

Hi all,
I'm a Ford Focus 2001 2.0l pertrol owner, and have been suffering from a worsening problem recently. I've been reading up and I'm beginning to think my lambda/oxygen sensor might be to blame - but I'd thought I'd ask everyone's opinion before I go out and buy a replacement! :lol:

The problem is that the engine has been stalling/rough idling. When I start the engine, it doesn't hold idle and just stalls immediately. I've learned to lightly press the accelerator to keep it at around 800 revs, and wait until it sorts itself out. This used to take no more than a few seconds, and all would be sweet for the rest of the day. But now I'm finding it takes anywhere between 10 seconds and over an hour to put itself right! I've learned to left-foot brake recently as I just cannot let myself take my right-foot off the accelerator for fear of a stalling engine.

The curious thing is what the engine does right when it sorts itself out: What it does is give a sudden burst of power, and then all is fine for the rest of the day! For example, I was once driving home, had been on the road about 25 minutes, and was cruising at 65 mph along the M11. Without moving my right-foot I suddenly got this burst of speed, taking me up to 70 in a few seconds! It then quick righted itself and I was able to drive normally from then on (no more left-foot braking at roundabouts etc.!)

So the clues I have are these:
  • Once the engine rights itself, it will be fine until it's completely cooled down (several hours later)
  • But the problem's not entirely temperature related, because I can drive for an hour and it won't necessarily of sorted itself out
  • It can sometimes be ok within seconds of starting the engine from cold, or not sort itself out all day
  • I was once told it might be a vacuum pipe to the inlet, but this hasn't fixed it
  • I've read that a faulty lambda sensor can cause a lean mix - which I presume can cause a cold engine to stall? Or a warm engine to rough idle?

Does anyone have any insightful advice or experience of these symptoms?
If it is a lambda sensor, any idea if it's the pre- or post-catalyst sensor? (I believe there are two, right?) (Can I inspect them to find out?)

Any advice will be greatly appreciated as I can't afford a Ford garage diagnosis, nor repair :(

Cheers all!
Thoric

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#2 Fiestaman1992

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Posted 20 September 2009 - 10:30 PM

the lambda sensor only starts reading when the engine is at a certain temperature, not sure exactly what but its when it gets hot. Other things could be at fault, maybe the throttle position sensor? idle control valve? air flow meter maybe, a number of things. i think you should use a diagnostics machine to see if there is any faulty sensors. sorry couldnt be of more help

#3 mintalkin

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Posted 21 September 2009 - 07:42 AM

if you can, get a 'live' data diagnostics done which should pinpoint your problem.

#4 Thoric

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Posted 21 September 2009 - 01:47 PM

Thanks FiestaMan and Mintalkin, I take it I need more advice from someone who can check out my engine with one of those OBD2 reader thingumajigs? I don't know anyone unfortunately, and I just know Ford will charge around 80 :angry:

Bit skint so I was hoping I'd diagnosed it correctly and could confidently fix it myself (least cost that way), but I wonder if I'll just have to face up to the fact I'm gonna need a professional. Bummer :(

#5 vinnyvangough

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Posted 21 September 2009 - 04:44 PM

I'd be drawn to thinking its the idle control valve

#6 Thoric

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Posted 21 September 2009 - 09:14 PM

I'd be drawn to thinking its the idle control valve

OK, thank you for your input :)

#7 SierraYankee99

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Posted 22 September 2009 - 06:10 AM

If you have breakdown cover get them out, they'll do you a code read free of charge to see why its cutting out. As VVG suggests its likely to be ICV

#8 Thoric

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Posted 22 September 2009 - 10:00 PM

If you have breakdown cover get them out, they'll do you a code read free of charge to see why its cutting out. As VVG suggests its likely to be ICV

That's a good idea - I do have cover.
So projecting forward. If this is the ICV, what am I looking at here? Dismantling the intake assembly? Cleaning and rebuilding, or new parts? I've not worked on an ICV before. Although I'm not averse to working on my car, this would be new to me. The most I've done before is replace the alternator, brake pads, wheel bearing etc. Is this possibly out of my depth?

#9 SierraYankee99

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Posted 23 September 2009 - 06:02 AM

Usually taking it out and cleaning it up solves the problem for a while but it will probably return. AFAIK a new one isnt too pricey and many on the forums I visit do it themselves. I'm not sure on the how to as I'm more conversant with working on diesels.

#10 Thoric

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Posted 23 September 2009 - 08:20 PM

Usually taking it out and cleaning it up solves the problem for a while but it will probably return. AFAIK a new one isnt too pricey and many on the forums I visit do it themselves. I'm not sure on the how to as I'm more conversant with working on diesels.

Well - I've taken a look at a Ford Technical Information System CD and it would seem one needs to de-pressurise the fuel system!? Or am I taking too much off my engine!? :o You see, it says nothing about a Inlet Control Valve, but it does talk about an Intake Manifold, and throttle body. Are these the same things? I really am beginning to think I'm outta my depth :(

#11 stef123

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Posted 24 September 2009 - 09:30 AM

Well - I've taken a look at a Ford Technical Information System CD and it would seem one needs to de-pressurise the fuel system!? Or am I taking too much off my engine!? :o You see, it says nothing about a Inlet Control Valve, but it does talk about an Intake Manifold, and throttle body. Are these the same things? I really am beginning to think I'm outta my depth :(


on a 2001 2l its not as big a job as you might think. the ICV is behind the inlet manifold so you have 2 options. 1. remove the inlet manifold etc or 2. remove the alternator.

personally i would just remove the alternator and go in that way, might be fiddly but it would save stripping half the engine to bits.

#12 Thoric

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Posted 24 September 2009 - 03:57 PM

on a 2001 2l its not as big a job as you might think. the ICV is behind the inlet manifold so you have 2 options. 1. remove the inlet manifold etc or 2. remove the alternator.

personally i would just remove the alternator and go in that way, might be fiddly but it would save stripping half the engine to bits.

Thanks for the advice stef123, I have replaced my alternator before so that's not too alien to me. I still don't know where this ICV is (other than that it's behind the inlet manifold), so I guess I need to do some more research. Anyone got any good links for websites with info (pics) showing things like this?

Oh yesah, will I need any replacement gaskets to do this? If so I'll need to get to a autospares shop before I strip the intake down because I'll have no transport options available to me once I do! :lol:

#13 stef123

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Posted 25 September 2009 - 08:47 AM

Thanks for the advice stef123, I have replaced my alternator before so that's not too alien to me. I still don't know where this ICV is (other than that it's behind the inlet manifold), so I guess I need to do some more research. Anyone got any good links for websites with info (pics) showing things like this?

Oh yesah, will I need any replacement gaskets to do this? If so I'll need to get to a autospares shop before I strip the intake down because I'll have no transport options available to me once I do! :lol:



just pm'd you mate.

looking at pm's ive sent in the past, did i not help you out with replacing the ICV a while back? you sent me the ford data?

#14 Thoric

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Posted 25 September 2009 - 10:34 AM

just pm'd you mate.

looking at pm's ive sent in the past, did i not help you out with replacing the ICV a while back? you sent me the ford data?


Hi stef! yes, it's me again! I replaced the vacuum hose last time and the problem went away for a while, but as it's back I was hoping it was something else, like the lambda sensor. That might have been easier to replace! :P

I've just checked and I still have your original PMs, so thank you again for the info you sent me! I'll just have to bite the bullet and strip that ICV. It may not seem like a big deal to most of you hardened petrolheads, but I'm pretty new to something this involved and really hope I don't screw up my engine permanently! :lol:

Thanks to everyone who's advised me, if I'm on here on Monday then presume it all went well. If before, I'm in trouble! :lol: :D

#15 stef123

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Posted 25 September 2009 - 12:46 PM

Hi stef! yes, it's me again! I replaced the vacuum hose last time and the problem went away for a while, but as it's back I was hoping it was something else, like the lambda sensor. That might have been easier to replace! :P

I've just checked and I still have your original PMs, so thank you again for the info you sent me! I'll just have to bite the bullet and strip that ICV. It may not seem like a big deal to most of you hardened petrolheads, but I'm pretty new to something this involved and really hope I don't screw up my engine permanently! :lol:

Thanks to everyone who's advised me, if I'm on here on Monday then presume it all went well. If before, I'm in trouble! :lol: :D


hope it goes well mate, its not a 'difficult' job its probably just more time consuming. where in the UK are you?

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