Apparently on date Mon, 16 Aug 2004 17:05:21 +0000 (UTC), "Paul"
<pauldotmartins@btinternet.com> said:
>Can duff oxygen sensors cause rough idle?
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.
>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.
Sounds reasonable.
>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.
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.
>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!
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.
>Any other obvious things to check?
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.