I have got a misfire on No 1 cylinder my 1995 300E diesel (55,000 miles). So I have stripped the top off the engine to get to the injectors.i intend to swap the injector with a known fireing one then if the misfire changes another cylinder i know the injector is duff. When I took the air intake off there is a vacuum unit bolted to the underside of the air intake it has 4 /5 vacuum takeoffs and two electrical plugs on it. On my car the insulation on the wires to this unit have got hard and broken off allowing the wires to touch each other. My question is what is this unit and what is the result from the wires shorting to each other? Apart from the misfire the car works fine although it do lack acceleration. Also the air inlet has a heavy build up of soot in all the passageways in particular No 1’s ports is this normal? Should I clean it out? Have I got a serious engine fault?