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!
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