My '90 has been running very well and I'm currently using it as my daily driver. It has however developed an issue.

When the engine is cold it does not have a high idle. It just goes directly to 800 warm idle. It runs ok but I know that there should be a higher idle until it warms up.

I have verified that the coolant temperature sensor is ok and I had rebuilt the AAV about 2 months ago.

Could it be the AAV acting up again? What does the ECU need to see to know the engine is cold and need to increase the RPM's and enrich?

Mark

 

Mark,

The cold idle speed is purely AAV controlled.

The CTS in conjunction with vac in that hose to the ECU, TPS position, all contribute to teh fuel map used by teh ECU.

The ECU on the Lucas system has no engine speed sensing.

I reckon your AAV is playing up again.

Find a spare at teh junk yard, and have it on teh shelf as a changeover, or remove it completely as I do.

 

I was afraid you were going to say that. I had completely rebuilt the AAV but I guess my fix was only temporary.

I have 3 or 4 AAV's laying around so I guess I will try again. I hate installing them. So difficult to get the hoses on.

What are you using in place of the original AAV?

Mark

 

Grant used nothing in its place! If it starts and idles OK, why worry about the high idle phase at all? When mine next goes wrong, it's coming off too.

Greg

 

Here ya go.

Only thing NOT visible is the SMALL hose that drip feeds JD into the inlet manifolds, and that gives some serious cold idle speed, trust me.

JUST KIDDING GUYS, JD is way too special for the Jag.

Well that went well, NOT. The file is 11.1mb in size, and this system only allows 4.77mb.

PM me your direct email and I will oblige.

 

For me its a matter of wanting to have everything operate as Jaguar designed. I realize that some of their systems are not very good but I know that when the car was new those systems operated as intended.

Like many of us here, I want to know how everything on the XJS is supposed to operate and how to fix it when it goes wrong.

Even if I decide to change a part or system for something better I want to make sure that I understand how the original system was supposed to operate. That way I will know that my modification will be a true upgrade and will not have unintended side effects.

Mark

 

Sorry. Double post. Nothing to see here. Please go about your business.

 

Mark,

If you google v12 aav there is a good diag writeup that might be helpful to you.

Thanks.

Jeff

 

I have a '92 with similar problem it starts and runs at 800 and as it warms up idle goes up to almost 1000.. whats up

 

me too. having an original is what i want not a rigged up vehicle

 

Douglas,

I have no idea where you call home, its not on your "sig", and since the V12's have different stuff for different markets, I will assume the basics.

Yours is a Marelli controlled engine. That system has its own little quirks, and I am NOT all that familiar with those components. They are SUPER reliable once sorted.

Having mentioned that, the cold idle is purely controlled by the AAV, and the slots that are opened when that valve is "cold".

Even the Marelli cars have no "idle control valve/motor", since that did not arrive until the last of the 6ltrs in the X300.

The throttle discs get coated in "black goo", and this upsets cold idle seriously, and also messes with hot idle somewhat. These need to be cleaned at every oil change (as a guide).

The rise in idle when hot on a V12 is considered OK, as the large mass settles, the oil thins to proper spec, etc etc.

Please dont misunderstand my scribblings, as I also like things "as designed", but sometimes that is beyond the tolerance of us mere mortals.

That AAV is a PITA, and even was so during the cars warranty period. I did heaps of warranty claims for them in the day.

All my V12's had that AAV deleted, purely for simplistic operation as daily drivers. I just got sick of that valve doing what it does.

I have one that I take care of, that still has that valve, and it sticks sometimes, does not close at other times, but the owner puts up with it, and I keep cleaning it out on an annual basis, and we are all warm and fuzzy.

Sort the AAV, clean the throttle discs, and then observe the goings on, and sort what is needed.

 

you will also find an ' extra air valve ' located on the right intake air filter body , this is an electrical switch that allows extra air in under certain circumstances from the filtered side of the intake filter ,

though mine is fitted and working, i still have to fully find out what it does and when, lol, this is in addition to the already mentioned AAV , which i had to rebuild and lubricate for good operation

idles at 1100 until the engine warms and then drops to a perfect 750 rpm

BB

 

I recall that it's wired into the a/c compressor circuit to compensate idle speed whenever the compressor is engaged.....which means it's operational at virtually all times. Might be easier/better to say that the valve *closes* when the compressor is not engaged so as to prevent idle speed from climbing too high.

Cheers
DD

 

Our market had that thing wired into the 15 minute timer fiasco.

It was so long ago I near forgot all about it. That thing was removed the 2nd dayI owned the car.