www.jec.org.uk

Chaps - my XJS started playing up a little bit recently and now it seems to have lost its fast idle completely.

It starts OK but only with my foot on the accellerator and for the first 10 mins of a journey it's prone to cutting out at junctions or whenever I take my foot off the accellerator.

Performance and fuel consumption are both about normal when warm but I'm wondering what's causing this fault...

It's a 1986 3.6 manual.

Many thanks

Simon R.

Hi Simon, sounds like the aux air valve is playing up (EAC7340 supplementary air valve).
Silly money from Jaguar if they're still available...best try Grublogger for a good 2nd hand unit.

best wishes

Tel

That was going to be my suggestion to, before you buy another you might want to see if you can bring yours back to life.

If you remove the end pipe of the aux air valve you can squirt in either carb cleaner or wd40 or something similar.

If you look inside you will see a barrel with holes, you can gently persuade a self tapping screw to fit in the center holesquirt in your cleaner/oil and let it soak, you should then gently be able to free off and move the small barrel inside by gently pulling and pushing in the screw.
Pop back on your pipe and see what happens.
You may need to adjust the hex shaped bolt on the side of the aav.
Hope that helps and not confuses.
PaulB.

Thanks for your replies chaps - it's good to have a fairly clear consensus of what's wrong.

Tel: great to hear from you again - hope your XJ-S is going strong!

Paul: I'll give that a go and see how it goes, then worry about a new unit later..

Two questions for you both though - what does the AAV look like? - and where is it?!

I took the S out for a nice drive today after I'd left it in the garage for about a month. I'd forgotten quite how much I love driving it

No need to start making hasty sketches of AAVs on the backs of envelopes - I've done an eBay search and now know what I'm looking for.

I'll nip outside just as soon as it stops blowing a gale out there and see if I can find it.

Cheers!

tried to find a pic and was going to suggest looking on ebay to see what one looked like.
You will find it by pearing into your engine bay from the passenger side, it is towards the front of the block at the top, inbetween that and the air filter.
2 big pipes coming off it.

Simon, unfortunately the 'S' is not playing ball. I have much the same problem as yourself, i.e. 'no fast idle'.
The damned thing is ok while cold, smooth idle on the warm up but as soon as temp rises all hell breaks loose. Backfiring, cutting out etc...

I have replaced the AAV and sprayed everything with WD40 but no change so far...

If summer returns this weekend ,as promised, I will have a look at the main ECU..

Why does it run smooth as silk when cold yet turn intro an unpredictable piece of sh1t when hot?....

Answers on a postcard....

Tel

Simon, unfortunately the 'S' is not playing ball...

Why does it run smooth as silk when cold yet turn intro an unpredictable piece of sh1t when hot?....

Answers on a postcard....

Tel


Sorry to hear it's not behaving, Tel.

I took my car to Jagutek for its yearly MoT and inspection recently, having written them a list of known problems with the car, and this not having worked since November, I got in, turned the key and it was behaving as normal again!

Bloody thing.

It's still playing up though - sometimes I get a fast idle, sometimes when it's warm it'll idle at 1,500 RPM.

If there's any future in substituting parts from my car to diagnose what's wrong with yours then you're welcome to pay a visit soon...

Cheers!

Injected the petrol tank with 5 litres of new petrol and couldn't believe the difference!
Started STRAIGHT AWAY and once warm, idled like a good un WITH NO SIDE EFFECTS.

Hmm. Petrol with a shelf life?

Ripped off Tel