ENgine management warning light (3.0l Petrol, manual)

[Benengo]

right, i fitted a replacement MAF this evening and its not fixed the problem 

so i decided to check again for suction when removing the oil filler cap. There was next to no vacuum. Unfortunately there was a bit of of mayonnaise like sludge on the underside of the cap which was not great. whilst i was look ing at the layer of sludge there was a single loud clunk/bang from the right hand side of the engine somewhere near the throttle body.... it was one of those sudden and loud enough noises to be pretty worrying! like a 15mm spanner being dropped from 20cms. Should i be terrified?

:'(

[Horizon]

Common for the 3.0i engine to have traces of mayonnaise looking oil in the rocker cover,  doesn't mean the head gaskets gone ,as for the noise, sorry can't help there.