Intermittent MIL Light

[CerbWill]

Guys I'm at the end of my tether with this problem. My Cerb 4.2 keeps giving me an intermittent MIL light and logged faults for Lambda 1 & 2, seemingly because the voltage from the sensors exceeds 1.8V. It started after I'd had the intakes & fuel rail off to repair a cracked cam cover. So far I've:

Replaced the lambda sensors.
Replaced coil packs. Took the intakes & fuel rail off again to change the packs, so I checked out the heat barriers & changed the o-rings to ensure a good seal.
Replaced HT leads.
Checked ignition using ignition lead testers that flash if there's a spark.
Checked 12v supply to lambdas.
Checked continuity of signal wire from lambda sensors to ECU.
Checked continuity to earth.
Replaced lambdas again with brand new NTK sensors.

Any ideas most welcome!

[CerbWill]

Thanks Martin, typically after having done this for a couple of weeks as I tried various things to fix it I've driven the 10 miles home without a single flash of the MIL light, lets see what tomorrow brings. I expect it'll come back, but the intermittent nature of it is pointing more towards a wiring fault that component failure in my opinion.

[CerbWill]

Maybe, although I'd have thought engine bay heat would have done that sooner. However, another 10 miles done to work this morning with no MIL light.

[CerbWill]

And it's back on today. Time to get the engine loom out of the car for a thorough check over I think. Might as well change the sensor connectors while I'm at it.

[CerbWill]

I think I've fixed it. The wiring to one of the connectors had been repaired before and didn't look in great shape. Anyway, new AMP Superseal connectors and all seems well. The peak lambda voltage is now much lower, about 1.30-1.35v. I guess that's still enough to tell the ECU the mixture is rich?

[CerbWill]

They switch fine. Before the voltages went high enough to trigger a fault warning they'd be up at about 1.5v for a rich reading, so I wondered if the slightly lower voltage reading I'm getting now would make any difference, but it seems not.