1990 Jaguar XJS - AAV Air Valve Confusion
 

Hello All.

I still have the original AAV (which works) so I'm not too bent out of shape

I received a used AAV from a member who was dismantling a Hess E car. Was excited as the AAV I have had a partly/mildly crushed wax ball on the bottom,,, something I did in the earliest days of working on the car before I knew about the GF FIX. Which I later did.

I've never had fine control of my idle as the idle screw was completely turned in which produces a idle in D when fully warmed of about 670-700 or so. In P, about 800+. I didn't and don't like that. As far as I know I have no air/vac leaks.

Anyways, I did the GF FIX on the AAV and internal clean on the "new" unit, even pushed the top hat in a bit lower than normal. I put the "new" AAV in and start the car, the idle cold is super high at start up. Way high. I plugged the hose going into the AAV from the filter case and it comes right down.

Looking at the opening in both valves side by side, not much difference. "New" valve will close completely when heated, but the amount of air going thru the unit is cold will never never do. Idle is just crazy at start up. Never even gave it a chance to warm up. Just tooooo high revs.

What am I looking at here? Is there a big difference that I don't know about between the HESS AAV and the 1990 HE AAV? Yup, I'm confused,,, again.

OK, my take on this from too many fiddles with this LUCAS item

AAV is the same, some have FINE thread Hot Idle screws, some have COARSE thread Hot Idle screws.
Some have slightly different "cut outs" visible through the Intake snout, never really paid much attention to that item,.

The Cold idle was around 1500RPM from new, TOO high for me also. The "setting" for Cold Idle was played with by ME, over many trial and error tapping down of the "top hat", until I was happy, and that is what formed the basis of the snaps in that write up. That unit is from the Green car, and the Cold Idle ended up at 1100RPM +/- a bees appendage, and quickly settled.
The Red car drove me nuts, and finally settled at 950 Cold, and obviously fully adjustable when Hot. I later removed that AAV and deleted that nonsense on all the V12's, too busyfor that stupidity. Separate write up on that, and Greg also has another take on that method since I did all mine a very long time ago, before Internet and Forums.

With HOT idle screw all the way IN, and the engine AT Temp, the engine will stall. I use 2 1/2 turns on that adjuster as the bench mark, and is usually so close as spit.

If you have plugged that Intake, and still out of whck my early suggestions are:

Vac leak, maybe
Throttle discs badly set.

A will assume?? that the air cleaner backing is installed and the 4 bolts are tight?? Those 4 bolts go through to the Inlet, and with them removed, HUGE vac leak.

Ha! Good Morning (here), Grant... Thanks.

I was thinking that ya might have a grudge against me for my hooping and hollering about ya at my SURPRISE in taking apart the ignition switch... MAN, did springs go flying, lol... Amazingly,,, following your advise to open it in a bag,,, I collected all the springs and got her back together.

It gets cold here in the winter,,, so I think the extra air is a must for the ol girl on them cold mornings. Hmm. I do remember ideas about some kind of manual choke but I don't think I'm ready for that yet...

Anywho. Both are coarse thread. But,,, I took the hot idle set screw from the old and put it in the "new"... The "new" came with no screw. Could be my issue right there....? I assumed (the dummy I am) that they would be the same. I'll take a close,,,, close,,,, look at the inside of the cavity's,,, and the shape landing pad where the base of the screw on the inside of the AAV would make it's seal today, after work.

Always something...

I THINK IM ON TO SOMETHING - FINALLY...

So, I went about the wonderful job of removing my delicate and super neat GUMMED up epoxy off the "new" AAV valve and thought I would have another go at it. With good results

Thinking about what Grant said, and having never liked how high my idle has always been at cold start, I decided to run the top hat of the AAV waaaay down, much lower than it would come OE. I had been looking at the old and "new" side by side and when I thought about it carefully (which I don't always do) I remembered that in alllll of my tinkering on this car that (adjusting the butterflies for instance) that a little air makes a HUGE difference in idle speed. So, with that, the difference in the opening between the suddenly seemed HUGE. And it kinda was.

Also, trying to get ahead of the high cold idle I went way down on the top hat. Maybe too far (we'll see once the weather gets cold),,,, and re-gummed it up with some quick dry epoxy and a new set screw in the side of the AAV casing. Good.

I just went out, installed it and started her up. BIG difference in cold idle start, immediately. GOOD!

Got the bright idea to reset the butterflies. When I let them go completely closed with idle screw bottomed out, just as Grant said it would, the car stalled. No air. Good!

Turned the butterfly adjustment screws one turn at a time after contacting the butterfly shafts and tried to start. Took a bit, and when the car finally did start at a super LOW idle I went and adjusted the idle screw. Idle came up and I FINALLY have real and accurate control of my idle. And it's REAL good.

I want to go back in with a feeler gauge (didn't have one handy today) to check my work.

The engine is running smoother and quieter than ever. I know it seems like I always say stuff like that, but it's true. I know my balance on the intakes had to be off due to the most fundamental mis-adjustments. Seems much better now. Closer and careful-er with a feeler gauge will be the next thing to do. What's the GAP at the top O the butterflies again?

Anywho,,,
Thanks y'all for amazing and continued guidance and support. No really! I mean it ☺️

Great job, JJJ. These engines really do respond noticeably to being properly set up and adjusted.

Well, well, well.

I HEARD your angst about the switch, even down here with the hearing aids OFF.
I learnt "selective hearing" when the kids were teenagers, mainly the Female of the species, and have fine tuned it even more now I am in my 70's.

I still have the final say in the house "YES DEAR".

I am with Greg, time and patience, a good alcoholic liquid top up, and these beasts are so simple.
.

They really really do, and it always surprises me. This massive engine,,, everything seems so heavy (hard to explain) and not so delicate,,, then all of a sudden you're dealing with .002 thousandths of an inch. In this case I would say a 6th of an inch more or less was what made the change in the AAV. .32-.36 V at the TPS, micro ohms difference in resistance here, then there, all matters.

It's an amazing shift in thinking I need to get things done. Especially for a hammer guy, lol... One day, maybe I'll have the courage to check the clearances in my VALVE set up - what a MONTH that will be, haha

Leave the valves ALONE!

Haha,,, I was hoping you could hear the sarcasm in my post in the other thread even with the hearing aids off. I figured they might be as you told me about the tactics and strategies you've adopted with the ear pieces, lol... Anyways, I was only kidding I hope ya know!

I'm not out of the woods yet, never am. I have a feeling the ol lady has something else in store for me related to this. Last time I messed around with the set screws on the butterflies I realized that I hadn't fixed the LOCK screw when I was driving down the highway (if y'all remember) doing 70mph and the throttle wouldn't close. Ohhhhhhhhhhh, that was an interesting few moments,,, and mile or two - over the Verrazano Bridge. Ohhhhhh the memories, lol
Need to find my feeler gauges,,, I know I left em around here somewhere. Wait, where's my instrument cluster, lol. My life!
​​​​​

Heck YEAH! lol

DO NOT upset the Jag Gods.

LEAVE THE VALVES ALONE until at least 1mil kms, and even then, NO.