An interesting fault developed on my 2.0 BMW. When warm the engine revs fall to 400 revs then climb to 2000 rpm and the engine fault light came on. I took it to my local garage and he eventually found the fault. The oil filler cap was not fully seated. It transpires the engine uses the maifold vaccum to suck the blow by gasses out and thus gave the symptom of a manifold leak.
Something to be aware of when checking your oil level. It just cost me £24 to find this out.

Go Bosch!
In the ever decreasing number of cars/systems that retain that Fuel cap pressurisation bodge. The Check engine light illuminates. To inform the driver of neglecting to screw the cap on adequately.