I have a 1990 Sierra 1.8 CVH. The engine idles uneven and there is a hiss from the underside of the master cylinder where it joins the servo unit. If I disconnect the pipe from the servo unit to the inlet manifold and block the pipe the engine idles perfectly. Does this mean a servo replacement is required.
Just to let you know that I got a servo from a breakers yard and the difference it has made is unbelievable. I guess the old servo had been getting gradually worse and then you don't notice how bad it has got. The engine runs smoother than it has for a long time and tickover is like a sewing machine.
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