My 89 v12 likes hunting revving to like 1500rpm then to low. Is there any way of telling what’s going on. I’ve recently closed my aav and looked at my TPS plug.

 

Welcome to the Forums.

Please do an Intro in teh New Members Area when time permits.

The list can be long, and I am assuming a Marelli car, as 1989 was teh change.

TPS out of range.
Throttle bodies way overdue for a clean and linkage reset.
PCV valve having a hissy moment, saok in paint thinners for a few hours and blow it out, you might be lucky.
Vac leaks, and that could be a days work tracking all the possibilities. Hoses, Inlet gaskets, hoses, over run valves (if fitted), hoses, etc etc.

Then comes the Marelli versus Lucas issues, and for that we need to know what system YOUR car is fitted with.

 

And.........?

What happened?

Could you clarify "closed my aav" ?

Grant is correct that the 'could be' list might get long, and you very well may have a stack-up of different faults that need correcting. But, the AAV is always a prime suspect so let's narrow down exactly what you done and how, and go from there.

Cheers
DD

 

I have had to 'synchronise' the throttles when that caused that fault.
If one is opened more than the other it causes problems.
Check for the same gap or listen to the pitch of the 'hiss' at each throttle to determine if they are even close.

bob

 

When I got the car it was revving high and I found a big hole in the aav bend so I repaired it thinking all the revving and hunting would go away I also cleaned the mucky from the butterflies and made sure all the things that should be connected is

 

What’s a PCV and where is it

 

I thought I’d check it for corrosion it just seemed a bit greasy TPS

 

I cleaned the but I never feelerd them + there’s blowing from the manifolds which I cannot hear a thing from the throttle

 

Repairing holes, good.

Remove the LH side air filter cover and the air filter itself. You'll now see the 1" hole in air filter housing that the big AAV hose connects to. With the engine running, cover this hole with your hand.

Does the up-down surging go away?



Good.

Makes sure the throttle blades are set to the correct .002" gap. Make sure that your linkages are not holding one throttle open a bit. Left and right must be just the same or you'll get surging or other weirdness.

Cheers
DD

 

As Doug's hole-blocking test will discover, it just might be a stuck-open AAV. When this happens, the symptoms are exactly as you describe. This is because there is a large air intake source through the AAV. This tricks the ECU into thinking the throttles are closed and the car is coasting from high speed, so it cuts the injectors to save fuel until the revs get below about 1300, then it starts the injectors again, the revs rise and so the cycling goes on. A new or repaired AAV is the answer. It can also be eliminated - but that is something for later when you are a real XJS fanatic!

 

I screwed the bolt all the way in and a little bit of high rev and hunting. I’ve since and the engine is maybe warm undo the bolt slightly more than what it was when I got it and it’s hunting from 500rpm to 1500rpm quite nicely but I don’t want the hunting

 

Remove the LH side air filter cover and the air filter itself. You'll now see the 1" hole in air filter housing that the big AAV hose connects to. With the engine running, cover this hole with your hand.

Does the up-down surging go away?

Cheers
DD

 

The pipe goes into the manifold not the filter housing

 

Look t item #4 in this picture.

https://www.jaguarclassicparts.com/u...alve-5-3-litre

Your engine should have this hose. One end goes to the AAV and the other end goes to the back side of the LH air filter housing. If you remove the air filter you'll see the hole that goes to this hose

Cheers
DD

 

I am clearly missing something here.

"I closed the AAV", which I assumed you blocked the thing off, but it appears you only repaired the inlet hose from the air filter backing to the AAV. NOT a vac hose, just an Inlet draft hose,and has NO affect on any hunting.

"I looked at the TPS plug", interesting??????

Have a read, maybe a combination f things that need some attention.

NOW, I am betting on a jammed AAV.