My Omega's engine management light sometimes comes on when under heavy load - usually when accelerating up steep hills. Had it checked and and it's the oxygen sensor. Haven't got it changed yet as 95% of the time it's fine.
I'm more worried that the engine doesn't tick over on idle as smoothly as I remember it did. Seems a bit lumpy now. Even to the point where the revs drop so much that it sometimes stalls, or the ECU over-compensates up to about 1200rpm. Can the oxygen sensor cause this? The engine management light never comes on when this happens.
Incidentally, I had a new airflow meter a few months back as that was diagnosed by the VX dealer as the cause of the light coming on - it seems to have reduced the frequency, but not eliminated it!
Change the sensor! It is used at idle when the engine is warmed up. I've noticed that some Vx cars throw a light on at the slightest hint of lambda sensor failure (wife's vectra 2.5) while my 24v Carlton's lambda sensor can die completely and it still doesn't light the ECU light!
Oxygen sensors are used to determine the fuelling strategy and if they are misleading the computer all sorts of things can happen.
But it's odd that they should be relevant at idle speeds.
There's other things like EGR valves, there are all sorts of tubes to enable the exhaust gas recirculation and if these tubes are plugged in wrong or incorrectly, they allow unmetered air to be sucked into the inlet ducts and this will definitely cause rough idle and lean running.
Similarly, air leaks anywhere else after the MAF will have this sort of effect.
The MAF as well can read wrong, they need to be cleaned regularly as crud burns onto the wires and makes a pound of air per minute look like two, meaning twice the fuel being pumped in for excessively rich mixture and faltering idle / bogging on hills, etc. On my car, I can clean the MAF in about a minute, two screws and a squirt of carb cleaner.
Sounds reasonable.
Well it's part of the system for controlling how much fuel to inject, so yes. HST, it wouldn't be difficult to have a situation where you can change the oxygen sensors and not fix the fault.
Chances are, the airflow meter just needed cleaning. I've seen one MAF that had failed, and I've seen dozens of MAFs that had crud on the hot wires and worked fine once washed with carb cleaner. They get dirty in use, the wire isn't hot enough to burn off dirt like, say, the oxygen sensor would be, and nobody seems to clean them during servicing.
Check there are no tubes or ducting leaking air into the engine intake, particularly the EGR. Usually this means a whistling, a drop of water on a leaking gasket or join will be sucked in and make a noise. This is a pretty simple DIY procedure.
Check it is all plugged in properly, i.e. the wiring is going to the various sensors and not shorting to the bodywork.
There can be silly things like injector leads plugged in the wrong sequence. Unfortunately, most faults in an engine will reveal themselves as a rough idle and that sort of thing so it's hard to say.
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