Experience Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.
Organizations Associate member SAE
EAA member
Publications Import Car magazine
Education/Credentials ASE Master Auto with L-1 certification up to 2000
Question have a 1984 xj6 the head has been replaced along with other things vacuum lines tune up etc. still has variations in idle timink maybe
Answer Hi Anthony,
The Series III XJ-6 is noted for having a rough idle even when everything is good. The rough idle is noted by feel in the car but not noted by any variations in the tach. If you see variations in the tach, then you may have a problem. One of many causes could be ignition timing or a vacuum leak but can be caused by many things.
Was it a Jaguar shop that did the head?
Check all the vacuum ports to see that they put all the hoses on including the one under the center of the intake manifold (hard to get to) Test the amount of vacuum on the vacuum port that enters the fire wall on the lower right side. Install a "T" fitting and measure the amount of vacuum at idle and let me know what it reads.
Do one test by pinching closed the vacuum hose on the distributor to see if it smoothes out any. Recheck the timing. Reset the idle mixture and idle speed.
