Faulty lambda sensors can cause rough running on M3Ws, especially at low throttle openings. This is because the ECU relies on their output to determine how much fuel to add for a given air/fuel mix in the exhaust. The lambda sensor used by Morgan is a Bosch 0258986615.
You could order a factory replacement, MMC Part Number E130007, but last time I checked these cost over £180 each in the UK.
Bosch supply a replacement kit with a 4-way junction block to attach it to your existing connector but many people find these a bit fiddly to fit and the connector blocks are quite bulky/unattractive as well as introducing another potential point of failure.
Therefore I have made up a few complete assemblies using brand new Bosch Lambda sensors and the correct connectors. All pins crimped with the correct tool.
I have made them a little longer than the factory ones to give some flexibility in how they are routed.
Price: £75 each or £140 a pair including UK postage.
Overseas postage charged at cost. Any local import duties are the responsibility of the buyer.
Please PM me if you're interested.