Idling Fast
 

My 87 US spec XJ6 S3 seems to be idling too quickly. Its running at about 1800 in park and about 1000 in gear. Warm or cold. It runs well, with only an ever so slight sputter I can hear in the exhaust. Sputter/slight miss seems to disappear when in gear. A bit of history as to a possible cause as it did not idle quite so fast before the "procedure". Car has 68k for mileage. I cleaned up the intake side of the engine including freshly cleaned injectors (Jag FI Service, FL), cleaned the carbon out of the (95% clogged) air rail tubes (for the smog pump) on top of the engine, and I also cleaned out the gunk at the throttle body and set the blade for .002" clearance. There was zero, as in no clearance before. I was thinking/wondering if that increase to the specified .002" at the throttle body is causing the additional rpm's. Like I said before, the car seems to run/drive well, it just idles too fast. I checked/rechecked for disconnected/loose vacuum lines. All seems to be in order. Aux air valve? I didn't have a digital ohm-meter with me (car is 100 miles from home) but I did have access to a non-digital one. I checked the resistance at the terminals and found there is little to no resistance. Again not sure of exact value due to no digital meter. I am getting voltage at the valve. I would find it odd (though not beyond the realm of possibilities) that the air valve would just go bad in concurrence with the clean fuel injectors, throttle body adjustment, etc. I didn't try adjusting the idle speed in any way via the 7/32" allen key either. I'm a little hesitant to mess with that. The setting for that hasn't been adjusted since it left the factory.
Anybody have any ideas on this? Can somebody inform me as to what the idle speed should be? Looking through various sources I get varying results as to what it should be. If memory serves, (note I haven't been "playing" with this car for a few years now up until now), it used to run at about 1500 rpm/park, 900 rpm/gear.
Thanks for any suggestions/ideas.
Dale

You only changed one setting, go back and see if that fixes the problem.

Idle speed spec, technically speaking, is something like 700 rpm in park/neutral but many won't run well that low (long story behind all that).

More common/practical/workable is about 900 in "P" when warm

1500 in "P" is way too high

You've have extra air coming from somewhere. A stuck-open AAV is a good possibility, or a leaky AAV hose. Try pinching off the AAV hoses and see what happens. They might be way too brittle to pinch down, though...and might just break. You could remove the AAV and just plug the hoses and see what happens.

I wonder if someone in the past set the throttle blade to zero clearance in an effort to solve/mask the problem?

No reason to avoid the actual idle speed adjustment screw. I mean, nothing bad can happen. Might be worth experimenting. But my gut feeling is that you have an AAV-related issue


Cheers
DD

Another wild thought: has someone advanced the timing too far? that would increase engine speed.

Also, my use of the term 'air leak' is a misleading. Better to say that you have 'unwanted air' coming into the engine.

Idle speed is controlled by air bypassing the throttle either via the AAV or the idle adjustment screw

Cheers
DD

The timing, or anything else for that matter, has not been changed since I have owned the car. I've never even bothered to check the timing, never since I bought car back in '93. The car was Jag dealer serviced by the original owner, so basically, I don't want to mess with the "factory" set timing. It ran fine (from an idle speed standpoint) before. It runs much better now with the fixes/changes I mentioned, but just too fast. I'm leaning towards the AAV as well, but find it a bit of a coincidence this valve would start acting up exactly at this point in time. I don't think I want to set the throttle valve back to zero. I would rather have it set correctly and track down the real problem, which, like Doug mentioned, might be the AAV after all.

I'm trying to locate the 7/32" idle adjustment screw. Looking at my parts manual (I don't have immediate access to car), group H, on the page with the Extra Air Valve, it shows a (EAC1737) "Idle Air Screw" in a "Block Assembly" (EAC1739). Is that it? I had been looking (incorrectly?) for something incorporated in the intake manifold itself.

The idle speed adjustment is in the 'air distribution block'...the small aluminum casting a couple inches forward of the throttle body. It has a couple hoses attached.

Getting to the screw is tricky. You'll see :)

Cheers
DD

Thanks Doug. That's what the parts manual is showing as well. A least I know what I'm looking for now.
Also, and I just thought of this as a possible cause for the high idling.
After taking the car out for the first time since it's seven year hiatus, I noticed the cruise control to be inoperative. The bellows are loose and can be spun around its housing. I have a replacement bellows, but didn't replace as of yet. Also wasn't sure how to replace. Question. Could the (semi) loose bellows be enough of a vacuum leak to cause the idle speed to raise that much? I would think not but as that vacuum line to the cruise is fairly small.

Dale,

Interesting question you pose. I've been struggling with a similar but less pronounced problem. Running great in drive and while idling in drive (no stalling or high RPMs) around 1000 give or take 100. However, in park, my idle is around 1100-1200.

I've been looking around at some of the more suspiciously faded or old vacuum hoses in the engine bay and noticed some were, as Doug suggested, almost too brittle to withstand a pinch or squeeze. There might be almost invisible cracking in some of the longer vacuum lines causing additional air to be pulled into the system. Just another suggestion.

Hi there,

I had this issue at work the other day on a series 3 and it turned out to be a sticky aav valve. They have a blade with a triangular slice taken out of it that moves up to open the gap up and allow more air and down to block off the flow. They have a nasty habit of corroding inside and a good clean out with something like air flow meter cleaner followed by a burst of inox usually sorts things out. Is the idle higher on startup and then settles down once the car is running a while? These things are meant to be controlled by the temperature of the water rail as well as ecu and if its stuck in the cold start position it would probably explain your issue. Maybe it was stuck before the throttle blade adjustment but is now evident due to it.

To be honest even during the late eighties things at Jaguar were pretty lax and I would not be surprised if the throttle blade was never adjusted right in the first place and the idle screw that you have been talking about was just adjusted to compensate for that. Don't be too worried about adjusting the 'jaguar' settings because the car probably would have been played around with in its first 6 years of life anyway and you cant trust that the the person who made the adjustments back then knew what they were doing, dealer or not.

Things like timing are worth checking because the springs in the mechanical advance could have snapped or stretched or come loose and the thing may be too far advanced as suggested. Or maybe the distributor is lose and has been knocked a bit. Stranger things have happened. I gather you have checked all the vacuum lines to the dizzy, climate control etc etc are all intact and not leaking? There is also a line to the charcoal canister and pcv breather as well. The line to the charcoal canister came off my car one day and caused issues. These cars always seem to run so rich that a small air leak actually leans them out a bit and makes the run better so you don't notice them as much as on modern cars that run far leaner.

As to the cruise control if the inlet valve on the bellows is stuck open and the bellows are leaking its possible this is your issue. After 7 years you never know whats happened, but personally ide be suspicious the AAV is stuck a bit to far open or if nothing else the idle speed speed screw was too far out to compensate for the misadjusted throttle blade.

Just my thoughts, hope they are helpful in some way.
Regards
Jay

Thanks for the responses to all.
I think I will try taking out the AAV and give it a cleaning as Aussie suggested. I was looking/shopping around for a new one, but the AAV seems to be discontinued. A used one is available, but not exactly inexpensive ($170). The Price doesn't exactly bother me too me but more so the fact that it a used unit. I will try cleaning it before I order a used piece.
Is there a gasket associated with the AAV? I could not find one while shopping around for the AAV. Also, does anybody know what size torx that is securing the AAV to the water rail? I have torx screwdrivers, but they will not work in removing AAV due to lack of space. A 1/4" drive torx socket is probably in order, just not sure what size.
I will also replace any/all hoses associated with AAV due to comments about age/brittleness. Probably replace as many other rubber vacuum lines for same reason.
I was/am on a quest beginning end of last year to do a "engine beautification project". Cam covers and exhaust heat shield sent off to Jet Hot for their services. The five air, vacuum, breather metal tubes I had chrome plated and buffed to a satin finish. Air cleaner, cross braces, intake elbow, battery frame and the breather housing at the front of the engine were all sent out to be powder coated a nice satin black. Air and fuel rails buffed to a nice chrome like appearance. The engine/compartment turned out very nice. I used a couple of pictures I found of Doug's burgundy S3 engine compartment as an inspiration. Damn fine looking engine compartment. Mines not quite to that point yet, but much closer than before. The "ratty" looking hood liner is really annoying to look at. Unfortunately, with no acceptable replacement available and Gonzo not making any more of his due to his illness, it will just have to wait.
I forgot to take a pic of my "engine project", but I will next time I'm up there.
Dale

One thing about these older Jags so many of the components are high grade and will last a lifetime. As often as not a good cleaning will bring 'em back to life for another couple decades. "Remove, clean, lubricate, adjust" is a mantra that will serve you well and often save you some money. Plus, for most of us, there's a lot of satisfaction in that approach.

If it does comes down to replacing the AAV a used one is probably a safe bet. They really don't outright fail all that often. Chances are you'd get a good one.



No gasket....although I vaguely recall a passage in the Jag service manual that erroneously suggests there should be.



Can't remember, sorry



[At least] one of the AAV hoses is unique....one end has a bigger I.D. than the other. Order your replacement hoses ahead of time




Sounds great and thanks for the compliment. Lots of satisfaction (and labor!) in engine bay beautification. I really enjoy the work. Upkeep after completion can be frustrating, though, and takes a bit of committment. That maroon Ser III I had was both my driver and my JCNA show car...so I was motivated to really stay on top of it.

I haven't done the concours/show thing for a few years.....and the engine bay of my present Jag is evidence of that :)

Cheers
DD

Thanks Doug! As always, you're the man!
Labor of love. You got it. Much work put into engine bay. Not to keep it that way. After sitting some 7 years, I took car out for a spin after reinstalling all the components. What was intended to be a quick take it around the block run ended up being more like 45 minutes. Id (almost) forgotten how enjoyable that car is to drive.
Finished up last weekend before returning home by installing the 7" headlight conversion I got from Andrew/Jaguar Specialties. They look nice! The was it was intended. Just don't tell WisDot on me.
Dale

I would also clamp off vacuum lines to see if you're getting unwanted air via these. The cruise bellows sounds like a good first candidate, plus any for the heater valve.

Another thing I thought of last night concerning the .002" throttle plate adjustment. I made the adjustment (was at 0, now at .002") with the throttle cable still attached to the throttle body. I seem to recall elsewhere the procedure called for the cable to removed first. Would this make a difference? I don't see how. I would think it would be more accurate to have the cable still attached, but I've been wrong before.
any thoughts on this?
Thanks.
Dale

No need to remove the cable for the adjustment unless it's sticky/binding, in which case you'd want to replace it anyway.

Cheers
DD

I am going to order a new throttle cable along with new vacuum lines and tubes previously discussed concerning AAV/distribution block. I don't think it's binding, but it might be nice to have a "new" looking cable to go with everything else that it looking new under the bonnet. How difficult is the throttle cable to replace?
Dale

An update to problem of idling fast. I rechecked the .002 clearance for the throttle blade and (my bad!), it was more like .004". Reset to .002". Took off cleaned and checked operation of AAV doing the hot water/cold water test, and it works fine. Replaced distributor/coil with Pertronix units. Now the car idles perfectly. Runs cold at about 1100/park, when warm runs at about 850/park and about 650/gear. Perhaps a tap low, but the car doesn't complain one bit. Only a very very slight "quiver". Very slight. This is the best the car has run since I've owned it/bought it back in '93. Very happy. The new throttle cable sticks ever so slightly. Not sure why. I seem to recall (not entirely sure, it's been 7 years since any real driving) the old cable doing the same thing. When using cruise, it occasionally requires a tap of the throttle to "release" the sticky cable for the cruise to resume correct speed. I do remember having to do that before.
Anyway, very happy with my "engine tune up and beatification" project I started last fall.

Good work, Dale :)


Cheers
DD

Thanks Doug!
It looks like I have a bit more "dusting" to do in a few areas. Ran out of time this weekend.