I would suggest buying a OBD 2 reader which costs about £10-£30 depending upon where you buy it. you can then read the fault code(s) and decide if its safe to use the car. If its the same code/sensor then I would get it changed.
Neil
+1:
I had an over sensitive lambda sensor, one of the 4 on a roadster. Kept on triggering the yellow engine light. Williams replaced if, not been a problem since.
Engine lights are triggered by data fed to the car computer. All Morgans have "custom", ie non standard exhausts. False triggers from lambda sensors are a common feature of modified exhausts.
You can get a nice little device that plugs into the OBD socket and talkes to a smart phone. Can't remember the details, will dig them out. But you can also get loads of mindlesssly interesting data out as well as cancelling lights....
