Been away on other stuff for awhile but have been reading with interest about vacuum issues. Specifically,... Why my XJ6, S3 idles rough in gear and fast (1000 rpm) in park. Having pretty much eliminated everything else, I just completed replacing old vac lines under the intake manifold and was wondering,... How can I test the vac regulator?
Anybody?
Thanks, Jim

 

Sooooooooooo,.. There is no way to test the vacuum regulator?

 

The intended function of the vacuum regulator has been oft discussed and not always entirely agreed upon.

Here's one person's take:


Function of Vacuum Delay Valve

Cheers
DD

 

How rough is 'rough'? A sight tremble, or more like a dead misfire in one cylinder?

If a slight tremble, well, some Ser III owners have been trying for years to be rid of it. Those who have met with any degree of success usually report that it was a stack-up of various issues, rather than a single fault, that were contributing to the problem. Slightly clogged injectors, leaking injector seals, valve adjustments a bit off, dirty throttle body, minor secondary ignition faults, worn distributor, degraded AFM signal, etc etc


What items have you eliminated from the list so far?



As for the 1000 rpm idle in "P".....

A vacuum leak or a stuck-partially-open Aux Air Valve come to mind.

Or, someone has set the idle up that high intentionally to solve a stalling problem.

On their best days these engines struggle at idle and can have a difficult time sustaining life. Now, for reasons not conclusively known (but often speculated on), *some* experience a unusually large drop in engine RPM in gear versus in "P", or with a/c compressor engaged versus not engaged. One expects maybe a 150-200 rpm drop in gear with a/c engaged but some will drop 300-400 rpm.....and the engine dies or nearly dies. Frustrated owners set idle speed artifically high to mask the problem....which they've probably pulled their hair out trying to solve.


Cheers
DD