Looking into buying an xj40 and the guy said the check engine light will come on and then go off after driving a while...mechanic said something needed to be cleaned ( he couldn't think of the name on the phone). I'm thinking the sensor but I could be wrong what do you think

 

Not a lot of info there boeing. Go see the car, sit in it and run it, when the check engine light comes on turn the car off. Put the ignition in the II position and push the VCM button, this way you will get the code and can go from there.