The cold idle is set to a degree, and does vary somewhat. About 1000 is common.
The "cut outs" inside the AAV determine that cold idle, and by carefully tapping down the Top Hat, will slow that cold idle a little, and aid the Hot Idle closure of the AAV. The travel of the Wax Bulb that does this, is not an exact science. Hence the comparison in that PDF.
Some AAV units have an alloy piston, some have a steel piston.
The alloy are well documented as jamming and scoring the bore. The repair people hone that bore, to clean it up, and also the outer of the piston, which CAN, repeat CAN, end up with too much clearance, and a Vac leak when closed.
The steel, so so common, but I have had a few bad ones.

The PCV is known as a "draft Ventilation System", hence the 2 passages you found. The weak part of that is the capsule filter under the Pig Snout. They clog quickly, especially with little use engines, and reek havoc. Remove it, replace the Snout and move on. Attempts to clean it have been less that successful that I know of.

There is an Extra Air Solenoid, in the grommet of the A Bank Air Cleaner. It is part of the emission system, and in some markets attached to a timer system. If it is Open, about 200rpm will be added to any idle setting. Some owners use it as an Idle Kick Up for the AC.

 

hmmm, yeah maybe i am hunting a ghost here. It just doesnt feel right driving with the idle screw all in. The emission control that shuts off the vacuum advance and gives some extra air for the cold start does not work. Its constantly in the "hot" state. I will not repair this, i will throw out all the valves and hardwire it in the hot state. But maybe the AAV is not 100% air tight and some goes through the throttle shaft sealings. I will leave it for now. I got a set of shaft sealings and change them when i get the chance, but for now i will concentrate on the rough idle.

I will check the plugs next and do the injector wire loom.

 

Today i checked the plugs:


the left one is from the old set...the "befor" state. The middle one is the after state for all plugs. Looks waaay more healthy now. it was really running very lean - hope i did not **** up the engine by driving like that.
The right one is the questionable cylinder - nr 6 at the right bank. Still a bit darker....so its getting a new injector.

 

Today i changed the injector and pulled the wire loom out. Here it is the bad boy:


While pulling it out i saw that my vacuum advance capsule has a adjustment screw at the back. Is it possible that my rough (and high) idle comes from too much advance at idle?

I did check the vacuum at the capsule and its at 12.5inHg as it should be, so the vacuum regulator is working correctly.
Now, what if the capsule gives too much advance at that vacuum. I read at another forum where Greg (the same as here?) experimented with different regulators. None of these gave 12.5inHG - so they are different for different emission systems.
I adjusted the timing on 18° at 3000rpm vac disconnected as stated in the manual (and inside the hood). Now what would i expect at idle with the vacuum advance? What range do i expect a smoothe idle?

I am always driving 98 or 100 octane fuel, do you recommend more base advance?

 

working on the wireing loom and i guess it was a good idea. Not sure if it was the reason for my rough idle but this didnt look good:


So i made it all new, just reused the plastic parts from the injector plugs since all plugs i got are too big. But the pins and all cables are new, i used 200°C high temperature silicone cabels.

Its almost done, just the plug is missing. it turned out nice, i am almost proud of it


When its back in the car i will see if it changed the idle....if not, i will check the idle advance and how much advance the vacuume gives.

 

So the new injector did not work at all. great!
So i put back in the old one and took it for a drive to test the wire loom. It works fine but didnt change anything.

I then tested the advance.
Without vacuum it runs at 0° at idle. With vacuum it runs at 20°. It doesnt run better at 10 or 15° so i can rule that out too.

So maybe it is the injector....otherwise i have no ideas left.

 

so update:
I got another injector and changed the one i suspect was leaking/running too rich.

nothing changed. same as always, slightly rough idle when cold, pretty rough idle when warm.

Im running out of ideas...maybe i check the valve clearence...that some are not fully closing? But thats a winter job

 

I checked the pistons with an endoscope. This is weird looking...not really carbon build up in my eyes. It looks more shiny and cristal shaped. And theres a lot of it. At the pistons but also at the chamber and i assume the valves too. I have never seen anything like this, but it might explain the rough idle. Any ideas what this is? The pictures are taken after a 350km highway run with speed between 60 and 160km/h.

 

So i had this other thread and it kinda got stuck:
https://www.jaguarforums.com/forum/xj6-xj12-series-i-ii-iii-16/idle-screw-all-where-does-air-come-291642/page3/
I did run it as hard as possible on long trips for over 1000km by now and still have this heavy build up in all of the cylinders as shown in the other thread.

I think the rough idle when hot is getting worse, not better. I have to switch to neutral at longer stops otherwise i get sick...seriously. When driving it feels smooth. But maybe i just dont feel it there.

I am really running out of ideas. I will do a leak down test again. the last one is a year ago and it was ok. maybe the running lean of the faulty fuel pressure regulatore ****ed something up seriously.....although the build up does not look like lean running.

 

I am no expert at this symptom but something tells me either the Fuel Regulator, or the AFM is causing it.

 

With all that rubbish in the cylinders it would not be not surprising if localised hotspots cause irregular idling.

 

Agree with Greg,

I am surprised it runs at all without preigniting.

Something in the fuel or additives used, dunno, as we are in the dark as to where you and the car are. The use of Kms and KPH suggests not USA.

 

Im in Germany, i usually run 98 or 100oktan premium fuel without additives. I used a injector cleaner additive and a valve cleaner additive a while ago (not mixed).

 

There you go. I see a heads off and combustion chamber clean in your future... Unless through the sparl plug hole you can grab a bit of the stuff from the piston and see what might clean it off.

 

Do you see the fuel as a reason or was it just misfueling from the bad regulator and not used enough in the past?

 

The use of additives can cause havoc in some cases.

While the intent is GOOD, the results can be far from that.

Whenever I use Cleaner, my rule is:
Pour it in with 1/2 tank.
Drive it HARD, NOW, not later.
Top up the fuel as needed .
300 or more kms is the usual, and HARD is the key.
Renew the fuel filter on return to home.

Too much "stuff" will, not can, screw the pump/s, filter, and anything else in the liquid side of the system.

They say Injector cleaner, or whatever, but it cleans EVERYTHING, tanks included, and that is the havoc that can result.

Not sure in Germany, but here we "no got" Cas and stuff, so the exhaust is basically unrestricted, so "blasting" stuff out on a Full throttle clean out actually does something.

Trying to find out what it is is a top idea, but removal might be a tad more work intensive.

I agree withy

 

Is there a way to get live fueling parameters while running? At least O2 sensor mapping at idle? Fuel trims would be a big help but I know this is prob motronic 1 or hopefully not k jetronic? Idk much about v12's, but fumes making you sick at idle sure sounds like overfueling, which is gonna cascade into taking out O2 sensors and cats if driven much (ref other vehicles). Must fix the cause of overfueling first as replacing sensors and cats first will result in quick damage from still present overfueling problem. Being able to analyze exhaust gasses or an ecm sure would be a big help. I at least have rudimentary access to the motronic in my '87 and 88 bmw's which is why I'm asking.

 

hey, i am not getting sick of fumes, im getting sick because the car is shaking so badly

Its not overfueling at idle, i did check the AFR on idle. My car does not have o2 sensors or cats. It was seriously underfueling a while ago due to a bad inlet fuel regulator, but i threw this one out and it feels quite good while driving. cruising at 150-160kmh is perfectly fine and it still pulls through quite strong at that speed. Its just the idle thats horrible. And it is somewhat uneffected by all means. For example fixing a massive vacuum leak (the vacuum reservour from the brake servo was missing, line simply open) or a broken vacuum advance capsule did not change the idle at all.

Yesterday my fuel selection valve in the trunk disintegrated and flooded my garage with 50l fuel.....yeah this just happenes if the tank is full. I replaced it with a T-piece for now and i have a bigger drive of 300km tomorrow.
Then i will put it into winter break, do a leak down test and then decide if i rip the heads off over winter. It only makes sense when the bottom is fine.

 

welcome to fight club,
my first xjs 1977 v12 had an occasional stumble rough idle. could feel it in the exhaust. drove me crazy.
i listened with a stethoscope ( long screwdriver) to all the injectors and they sounded the same.
by pulling the injectors I could make the stumble more consistent. so i figured spark. took the dizzy off and rotated engine in the range of the offending cylinder.
because of the advance system you can rotate the distributor rotor a little bit. by barring the engine I set the the dizzy disc with the pins that activate the pickup that I could spark that cylinder. it worked perfect..moving the rotor clockwise and ccw just moved the pin from that cylinder pass the pickup. Then I got lucky. I changed hand and suddenly it did not work. there was some radial play in the dizzy shaft and sometimes the disc was a hair further away from the pickup and did not fire that cylinder.. like I said I was lucky. adjusted the distance to the sensor a hair closer and the engine ran smooth. better men then me would have replaced the dizzy with less wear on it but it did the trick for me. it took me 6 months to figure it out and then again luck had a hand in it.
it is a long shot but you can try.

my 1996 landrover disco 3.9. had a similar rough idle. adjusted the gap and it was gone. both British, both old and abused. don't know but it worked.

good luck.
j

 

i did check the signal from the pickup with an oszi and also checked the spark signal - all are smooth and consistant. Also checked the spark distance wich is aprox 15mm. (interesting: i have a stringer spark with the original twoncoils than with a new "high power" coil) so i rule out the ignition.
I also checked every single injector signal with the oszi, they are all fine with a clear peak/hold signal. even rebuilt the injector wire loom.

One injector seemed to have to much flow or slightly leaking because the plug was a little bit darker, so i replaced it. now all plugs are exactly the same. Still no change in idle.