Ive received the parts to restore my aav today and have read a few threads where people have pushed the top hat down a bit to improve tickover speed. I haven’t been able to get a definitive answer on how far in to sink it. To anybody who has had success with this am I anywhere near in the photo or does it need to go down a bit more. If your about Grant I would appreciate your thoughts please !

 

Grant will tell you to get rid - wait and see

If your tickover can't be set using the 'bolt' at the bottom something else is wrong and you're treating the symptom not the problem.

AAV Remove

 

Maybe I've worded it incorrectly regarding tickover. The car is hunting upon after start up and I'm sure it's down to the aav. I just want to lower the initial warm up revs as described by others by lowering the top hat into the aav body. As I know grant has done so, I was trying to get an idea of how far down it needs to go.

 

Quite correct Brinny.
Ben, the AAV is a very approximate thing at the best of times, adjusting the position of the top hat (ie adjusting the size of the wide open position) is a very well trodden and effective way to fix the too-high revs at cold problem.
I would look into the side air entrance tube, and push down the top hat just enough to where it starts to taper, and try that. If you tape up the thing in place with gaffer tape or just an easily removable bead of silicone round the join, then you can adjust it to where you want it before finally epoxying it.

 

Hi Greg

I've got the same problem!

When I do a Cold Start, She runs away at 1800 RPM so what I have been doing is foot on the Brake and in Reverse as soon as possible and then Reverse her out of the Garage ASAP and by that time the Revs die down to about 1100 RPM and then on down after that to about 700 RPM

I've never heard about pushing the 'Top Hat' down and didn't even know what the 'Top Hat' was, as the Car always ran like this ever since I bought her from the previous owner years ago and so I never gave it a thought that anything might be out of kilter, as the meticulous previous owner used to have her Serviced every 6 months! so no wonder that I now steer clear of Garages and Shops

So how do I go about pushing the 'Top Hat' down?

Do I just push it down with my Fingers or will I need to push it down with a Clamp or maybe even give it a 'Tap' with a FBH

 

Ok, OK,

IF that is a snap of YOUR AAV, then that is about where I have them tapped down to,.

As Greg mentioned, no 2 AAV units are the same, like women.

The snaps in that PDF on here, are what I generally look for via the Intake snout.

It is a trial and error thing for sure, so many, many beers.

If its hunting at Cold start, it may not be totally teh AAV, as also mentioned.

I aim for 1000RPM cold, it just sits well with me. The Red Beast was 900, until I ditched that fiasco, now the solenoids have me at 850 Cold and I run 650 HOT.

ALSO

I have that HOT IDLE bolt set at 2 1/2 turns OUT from fully home as a starting point, and never had a "hunter". Adjust the HOT idle once its HOT.

 

Alex
Grant has a paper on the AAV and how to fix it, I attach a copy but emphasise it is Grant's expertise, not mine!
Of course, I believe a better solution is to make a solenoid operated fast idle system. This you already know, but for new readers I also attach the paper I wrote (complete with GiF hand done diagrams of Leonardo standard of graphics) of how the AAV works, and what i did to make a solenoid fast idle.
How long does it take for your 1800 idle to drop to 1000 though? If only a few seconds, say 15 or 20, then it sounds to me more like a sticking butterfly,as the AAV does not react all that fast.

 

Thanks Greg and grant. Yes grant that is a snap of my aav. Just going to replace the piston spring and a new bulb and try it. Wanted to hopefully be in the ballpark before re assembly. We will see.

 

Hi Greg

Cheers!

Although I can see what you mean now, I don't want to risk it, just in case something goes wrong (broken bolt or stripped thread etc) and I go and make things worse instead of better

Which I do not want to do, with Summer just round the corner, though it hasn't turned up yet

The AAV is quite Slow to react, which has me thinking that its working properly (or maybe not?) who knows

So when I Start her up from Cold, as soon as She fires up at 1800 RPM I get her into reverse gear as quickly as I can, which goes in with a 'Clonk' and then back her out of the Garage which takes a couple of Minutes as there is a bit of a tight left hand turn to go round

By the time I've done that, the idle is down to 1100 RPM when I put her in Neutral (which I feel is ok) and then starts slowly going down to around 700 RPM from there

Where my only real main concern is I don't want the Engine roaring away at 1800 RPM the moment that She Starts, before the Oil Pressure has had a chance to build up

No Vacuum leaks or anything, so I'm staying in the 'If it ain't broke don't fix it' Camp for the moment

Unless there is something 'less risky' that I can try? or Paranoid me might just not be able to hack it!

 

Check the thottle butterflies for 2 thou/any dirt/crud build up. I reckon something is jogged shut after bit of running. I agree 1800 rpm on start is far too much.

 

Hi Greg

Cheers!

I will try that but it feels like Winter this morning, so having a chance to play Catch Up with stuff around the house

 

As will Doug 😁

Although my final solution is different than Grant’s.

Cheers
DD

 

That's about the worst possible thing you can do to the transmission. It shock loads the clutches and pretty soon it will tear out the teeth of the clutch plates and you'll have no drive. The power transmitted by a torque converter varies by the square of the speed, so going from 900 to 1800 RPM doesn't double the amount of power the transmission has to absorb, it's 4 times.

Something isn't right with the way your idle is set up, I'd fix that first, or let the idle come down on it's own before putting it in gear. My personal rule of thumb is nothing over 1000 RPM before engaging a gear. Unless you enjoy rebuilding transmissions that is!

 

Hi Jagboi

I was wondering about that myself, as I can feel that Shock Load, when I put her in gear

Do you know of any 'Hack' that can get the Revs down on initial Start Up, rather than risking a Broken Bolt, or Stripped Thread by trying to take the AAV off, this side of the Summer

Once She's Warmed up then She's OK for the rest of the day

 

Daft as it sounds I'd plug the AAV and see if it really is that, some strong and really sticky tape to restrict the AAV intake or even pipe clamps on the hose if it isn't in bad shape ?

Know how you feel - last time I parked I had no idea it would be 18 months and counting before I ran it again = I'd settle for it running this summer !!.

AAV and airleaks at the manifold to head joint were my problem when I had this problem. On the upswing it went real high and on the downswing I had to tap the throttle to stop it dying - some of the nuts on the inlet manifolds were barely finger tight - some not even that tight. There's a huge list of places that air can get in where it shouldn't, once I started the tear down on mine I found at least three places where it had been sucking air for sure - one was the vac hose to the back of the car, the manifolds and the stabbings for hoses rear right of the engine. I also found the injectors to be full of rust and crud so that didn't help.

Not saying you have an air leak but it would be easy to set one of these up to tickover nice but the air isn't getting in where you think - so the AAV is like starting on half throttle when cold.

Advice on the auto trans is totally valid - don't do it -

 

Hi Ben

That's not daft but an interesting idea!

Which I will look into, as from a practical point of view, it looks like that might work



Which one of those Pipes should I block off?

The Straight one at the Bottom or the Curved one on the Top?

Then at least I'll know if the AAV is the cause of the problem

 

I'd probably go for the bottom one - I would be looking to limit the influence of the AAV whilst leaving the hot aisle circuit functional as much as poss. You could close down the top one though just don't close it down completely and don't underestimate the power of a good 'suck' - I'm sure it is part of the problem.

 

Caution required in restricting the AAV hose….the one from the back of the air cleaner housing. You can end up with the innards of the distributor totally soaked with engine oil.

(Please don’t) Ask me how I know 🤓

Cheers
DD

 

Hi Doug and Ben

Feeling slightly confused about which hose I should be putting the squeeze on, as I don't want the distributor soaked in oil if I do the one that's at the back of the Air Cleaner

Or should I close the Top Curved one down instead

Not sure what you mean about under estimating the power of a Good Suck?

Do you mean the suction from the Engine or do you mean Suck on the Hose with the Engine Switched OFF to Test for Air Leaks?

 

I've never understood why Jaguar pull air through the distributor - seems a bid daft unless it serves a cooling purpose -

You do not want to block this entirely - unless you can plug the AAV after the idle bypass - negate the influence of the slide. If you close the outlet then don't close it completely - just restrict it - the goal is to remove the influence of the slide but leave the idle bypass functional.

And by suck it was intended that you understand the forces air can apply - make sure your restriction cannot be sucked into the system.

If I was doing this I would print a plug that was a slight interference fit in the inlet with a bolt in the centre to facilitate removal - make sure it is in far enough to negate the open port of the AAV but not mask the idle bypass - mine is back on the engine or I'd take a pic. This is only to show that the idle settles low from cold.

I would still be looking for air leaks too - carb cleaner or stethoscope - RPM's need air