There are many threads about rough idle on AJ16 engines, and just as many fixes.

Mine is a 3.2ltr, Australian spec, so NO EGR, or much else for that matter.

Intermitant rough idle since I owned it.

1) O2 sensors, small improvement, then out of the blue rough as again.

2) Coolant Temp Sensor, big difference.

3) Oil cap seal, better again.

4) Crank Angle Sensor, due a NO GO, but no real change in idle.

5) Spark plugs, just because.

6) Intake trunking replaced, looked a tad old and stressed.

All sorts of other bits and pieces, systematically, mainly from a service point of view just to get the car up to my standard.

Been acceptable for quite some time now, but the last few days getting "hissy" again, and mainly a 20-30rpm deflection, as it warms up, and as it gets closer to "N" it settles significantly.

Yesterday was oil change day, big deal, but I do the oil filter from the top, so the trunking elbow comes off for that bit, and on the plastic elbow that has the air temp sensor in it, and the breather hose attached, I noticed an oily witness mark on the "plastic weld" of the "muffler" thingy that is part of the elbow. Closer inspection found that the weld was split, maybe badly made, maybe from my pushing and shoving (doubt it), or just plain "old age".

I applied some RTV as a temp fix just to suss it out, and surprise, surprise, it worked, the idle is as smooth as the V12 at ALL times, no more "hunting" at any time.

This part is serious $, and not much will really stick to it, and rewelding it is a no-no in my opinion, so I cut the "muffler" off, and JB Weld attached a metal cover to the short spigot remaining and painted it so it looked good.

This morning was the test, and cold start was as normal, and I waited for the hunting to start, usually after about 1-2 minutes warm up running, but NOTHING, all smooth and stable.

So once again, un-metered air in the system, and strange idle. These new style engine management systems are very fussy about these things.

 

jb weld is a great product

 

Yep, many, many of my Jaguar bits are held in place with it.

The front carby bowl on the MK10 was done with it 15 years ago, and is still fuel tight, good enough for me.