1987 5.3 v12
Im working thru some problems, one is my idle is steady at 1200 rpm.
I completly plugged the aav, checked all vaccuume lines, set the throttle linkage, and sprayed around everywhere with carb cleaner with no change.
After a lot of "tweeking", I got it to about 800 in drive, but the aav is completly plugged.
Could the overrun valves be a source of a vaccume leak?
Thanks, Pete

 

I'm in the same boat. 1990 XJS 5.3. Replaced both O2 sensors, both fuel pressure regulators, air temp sensor, water temp sensor, EGR valve, EGR valve solenoid, both igniters. All new parts. Adjusted butterflies, cleaned throttle bodies. Idle Air Valve was replaced by previous owner not too long ago. As was crank sensor. Screw is all the way in on Idle Air Valve. Verified both A and B banks have combustion. No matter what I do, same 1200 RPM. Drops a little lower in gear. Lots of air through B bank filter housing (driver side). Very little through A bank (right side). Don't see any vacuum leaks. Vacuum lines replaced by previous owner. Looking at TPS next and maybe taking off and inspecting Idle Air Valve even though it is new-ish. Anyone have any other ideas? Thanks, Scott

 

Well, I pulled the over-run valves and they looked O.K. Going to make blanking plates.
Next step is to look for proper TPS adjustment.
Pete

 

Just a thought, apologies if this is obvious to you, but have you blanked off the B bank airbox inlet from the AAV at the manifold itself? It is quite easy to block something but not the actual airfeed into to the manifold.

Air is getting into the manifolds somehow, that is for sure, so I suggest a pleasant morning spent as follows: If you remove the airbox outer cover and filter each side, carefully plug ALL the extra holes you find. Then remove the balance pipe across the rear of the engine and block those inlets to the manifolds. Loosen the butterfly spindles and push them closed. Check the throttle bodies underneath where there are tappings and spigots of various sizes and close them off too. The hoses to any tappings may be leaking, so close off the actual fitting, even if it has a hose on it. You will find it!

Greg

 

are the TB's butterflies set to 2thou ?

any more and the idle will be high without any other issues effecting it

at the end of the day treat it as a sealed system , any leak or open hole will allow too much air in ( not teaching anyone to suck eggs though )




just pointers

BB

 

Great advice from both of you!
Yes, I am sucking eggs! I haven't found the leak!
I machined a delrin plug and shoved it in the AAV inlet.
Never did check the connection at the brake booster!
Unfortunately, I have the fuel tank and surge tank out now, dealing with the dreaded rivet, and cleaning things up there.
New hoses, filter, pump, just going thru stuff.
You both have great ideas, when I think I have "thought out of the box", and covered everything, you bring new ideas to the table!
When all is tidied up in the trunk, I have a new conviction in the engine bay!
Pete

 

I've got the following problems ...

1. 2000 RPM (!) idle,
2. Car is running rich as can be, fuel mileage is suffering badly.

No missing or running problems, but I can let the thing idle down the road at 45 mph, which is kind of scary. And, under braking, I'm braking against the engine trying to push the car faster.

It's like the car is stuck with an open choke. Looking for ideas...

Jess

 

people, dont forget to check for missing throttle body bolts and tighten up your intake manifolds!

Jess, check out your fuel regulator, AAV, and maybe have a look at the timing as well

 

I miss you big time bro. I will finish the Jag for Katie.

 

I too have a high idle issue 92 xjs v12 convertible, runs at 1200 rpm (like others on this post), 58000 miles bought from an estate a week ago. car had been undriven since 2009 started occasionally by the son. Car has a check engine light as-well, with fault code FF14. I changed sensors that were part of code no code anymore but still check engine light (CEL) High idle is issue I have closed AAV bolt all the way with no change. I would assume the ECU is getting a signal from something telling it to run high. What are the common causes found by all the forum members regarding high idle. has anyone had the AAV rebuilt? there is a guy on Ebay doing it for $75.00 + shipping anyone use his service? My goal is to fix the problem not to bypass things. Oh just a side comment I removed the sensors that came on car (looks like LUCAS brand) Bought two lucas brand temp sensors, both broke when i gave them maybe a pound of torque. the originals look the same but don't break $60 down the tubes Is all LUCAS junk?

 

i see lots of throwing parts at the problem to solve. I know there is a group of owners out there that know exactly what is wrong. Veteran owners I need ya!

 

The 'could be' list is long but if you have a V12 with a high idle and you eliminate a mechanical fault (like a binding throttle linkage, incorrect linkage adjustment, or such) then you've got unwanted air coming in from.... ** somewhere **. That's where the 'could be' list starts growing.

Stuck AAV, throttle blades not gapped properly, bolts loose at air filter housings, vacuum hose leaks, etc.

Cheers
DD

 

Hey Doug (great name) The engine bay is super clean, 58000 miles I have checked all obvious vacuum lines and such with no avail. the seller was surprised to see the check engine light so I assume it was caused from maybe it's lack of use for close to 6 years. when I start the car it will make a sound like a high pitched whistle that doesn't persist. sounds like air moving super fast, but can't seem to isolate problem. Can AAV be unstuck. have you heard of the rebuild service on ebay.
Thanks Doug...Doug Powell

 

It's taken me this long to get around to fixing this problem -- having the idle stick at 2000 while following a road-paving crew, then baking the brakes trying to hold the car back, losing all control and having to put it into a dirt pile to get it to stop will wake you up -- but mine was apparently the AAV. I'm having it rebuilt now.

...and getting new brakes.

Jess

 

I did not read all the posts but I also did not see anyone mention IACV. Usually the issue when you have high idle.

 

The AAV can be unstuck, usually. Search for some postings by Grant on the subject. I think he has a good DIY write-up

Cheers
DD

 

No IACV on the older V12s. Well, the AAV we've been mentioning is sorta the same thing.


Cheers
DD

 

Mine had a high idle, and I went through the usual suspects: AAV, throttle linkage rods, throttle cable, adjust throttle stops and blade clearance etc.

Turned out the return springs under the manifold at the throttle plates were weak. New springs cured the high idle. if I was in traffic and eased off the throttle it would stay at high idle. Put it in neutral and blip the throttle and it would come down.

 

I just purchased a 95 XJS from a dealership, it had been sitting on the lot for a long time, ran great for a couple of days then, when it was cold and first started up ran fine then when you shut it off and restarted it, it would automatically go to 1300 rpm in park or neutral, drop it down into drive would run at about 7 or 800. Well, I first thought it was the Idle Air Control Valve or the throttle position sensor. I cleaned out the throttle body the MAF sensor and put in a new air cleaner. After doing all that, it still wanted to Idle High. The last thing I did, was go to AutoZone and bought a can of Gummout Expert Injector Cleaner, filled up the car with fresh gas and added the cleaner, the car is doing a lot better now since I put the Gummout in the tank, the rpm's are coming down as I drive the car, almost where it's supposed to be, I think it will probably be back to where it's supposed tlo be in about another week if not sooner. After sitting on the dealership lot for a long time everything gummed up. Hope this helps someone out there. Happy Motoring

 

I have had the same problem after working on mine for the past 3yrs, drove me crazy and many post for advice. came down to 3 areas on mine, and with checking and looking, and listening came across these three things

1) TPS- even though I adjusted and had a good reading, I rechecked and it was below what should be, I think it was around .25 tried and tried to adjust to no avail, put on new TPS adjusted and stayed on target

2) connecting hose on balance pipe, on the B Bank there was a very slight leak, loosened clamps, and reseated the hose, tightened clips.

3 ) I had a new AAV, tested it before putting on and was good, even after doing 1 and still had a high idle, 1000 rpm, decided to remove the AAV and recheck, and it was not closing properly. I still had my old one so cleaned it out good with carb cleaner and then with some penetrating oil. tested it, and adjusted it a bit at a time until it closed (did go a bit much on crimping the bulb) now it opens about half way, put old one back on stared the Old Girl up, idled at a round 950 to 1000. . when warmed up idles at about 750 to 800 rpm.

The is no hesitation or pinging at all and runs great