Changing a lambda sensor - any tips?

[r.welfare]

The wonders of modern(ish) motors. The Avensizzzz has been putting it's engine light on occasionally of late, and has also been surging a bit on a light throttle once warm. Makes cruising at 50-70 (as it corresponds to 2-3k rpm) a slightly annoying experience.My code reader has identified two codes, to do with one of the cats not operating at peak efficiency and one of the lambda sensor's heating elements (P0420 and P0430 for OBD fans). Economy seems good still (37mpg, not bad for a 2-litre petrol), and it picks up fine when given plenty of throttle. No rattles from either cat.It's got four lambda sensors, so I've been disconnecting the power to each one on an individual basis then going for a drive to try and identify which is duff. This morning I think I hit paydirt in identifying it's the pre-cat sensor on the nearside - the surging has gone, and two new codes appeared, commensurate with the disconnection of this sensor, but not the same codes as before. So I've ordered an OE Denso sensor from ECP, together with a special 22mm socket with a cut-out.My question - how easy is it to remove one of these things, given that (I assume) it's been in-situ in the manifold for the last 8 years and 126k miles, subjected to a fair amount of heat over that time? Is a good squirt of WD40/Plusgas the night before a good idea? Am I at risk of shearing it off at all, and does the new one need sealing with anything when it goes back in?

[Pillock]

When I changed a lambda in a Mondeo that had been in since new, at 10 years old, I just put the socket on it and gave it a tug. It wasn't at all tight, but they're a hefty lump of metal so wouldn't think you'll shear it.

[red5]

Soak it and away you go. Generally the welded on bit the sensor screws into is of higher grade steel than the rest of the system, so less prone to internal corrosion. The sensors usually have a compression washer type seal or interference fit, similar to spark plugs.Is the problem there all the time? or does it appear when hot/cold?

[r.welfare]

It only really seems to surge when warm - it's fine when cold but this may be due to the overenthusiastic enrichment (it idles around 1400rpm when stone cold, dropping gradually to about 650rpm when warm). Warm idle seems quite low to me, but it's within tolerance according to Haynes.It's a bit like a very gentle misfire, and only occurs under light load between 2k and 3k rpm. Above 3k it's much smoother. Idles perfectly smoothly as well. Spark plugs just changed a couple of weeks ago with the proper Iridium Denso jobs as was the oil and filter - the fuel filter is next on the list to be changed (although the existing one doesn't look that old). No obvious air leaks, air filter nice and new, I've cleaned out the throttle body with some carb cleaner as well. No MAF or EGR on this engine, apparently, which would be other suspects normally.

[CIH]

It's easy to twist the wires while winding it down on the threads. Either unplug it from the loom if there's a handy connector or or softly pre-twist the wires counter clockwise a little so they unwind as you tighten the sensor. Not thing too tricky, they're just a little brittle. Like a sparkie.

[meggersdog]

Yeah what's been said already.I know you've ordered a new one but did you check both the negative wires for continuity.There are two black wires and I don't know whether it is to do with the heat but often it is just a broken wire.Always one of the black negative ones.Because the sensor comes with wires attached replacing it cures the problem.