Car started OK but idle a little bit erratic between 600-1000 went shopping drove OK, normal idle at lights etc. revs dropping slightly while parking, ride home again OK though no traffic all lights green, however since arriving home engine idle has become wildly erratic.

On engine start the revs start at just over 1000 then settles to 800, thinking ok then, then revs drop down to 500 then surges up to 900-1100 this keeps repeating till the engine finally stalls.

Cleaned breather hose from oil tube to intake elbow, was really gummy, cleaned & replaced, still the same.

Any ideas

 

Hi Philip,

My first suspect would be a leak in the air intake between the Mass Air Flow sensor and the intake manifold gasket, or in the crankcase breather system, or a problem with the Idle Air Control Valve.

Cheers,

Don

 

I'm in agreement with Don B. I would add one additional potential cause; a de-laminating harmonic balancer.
Your car, at 27 years old, is approaching 30, how many miles? De-laminated harmonic balancers with Jaguars of this vintage is a common problem.

 

My delaminated balancer didn't affect the idle speed or cause the engine to stall, it just caused children and small dogs to run to their mamas holding their hands to their ears. (not the dogs of course)

my vote vacuum leak

Larry