Hi,
I forgot about this thread. It can only be a failed sensor / coil or more likely a bad wire/ connection.
I had the same issue and after nearly 2 years of chasing it, I eventually found the problem(s). Well there was a few but you'll see below what I mean.
The idle control valve had open cracks on both hoses going to and from it.
you can just make out this little hole.
I gave the whole car an overhaul in wiring, following each one, checking its connection and making sure its not broken or corroded. I found this on the MAF wires under some wire insulation. The MAF still worked but who knows what kind of faulty readings it may have given.
However, my biggest find was when I checked the relay's and the fuse box.
I looked under the 3 relays on the left of the fusebox there and found 2 broken wires from one of the relay, I was delighted to find an actual problem.
So I looked into what the relay controled.
Its a double relay, the first part gave power to O2 pre heaters. When cold, the o2 is ignored but while that is happening the o2 sensors which only work at high temperatures require electrical help, so they are preheated to bring them up to temperature quicker. This never happened on my car and the o2 sensors where not giving correct signals.
Secondly, this same relay also gave power to the ECU to say turn on the AIR pump valve and that the O2 sensors are preheating.
Once I got these fixed. Problems I had simply went away.
I hope you can get this sorted soon but do give the wiring a good looking over.
Baz.
