So my 88 XJS V12 had been sitting for about 4 weeks, while the AAV was being repaired (Great job by John John!) I tested it in hot/cold water, and it opens/closes exactly on spec.
I put in the AAV yesterday, engine stone cold after four weeks and ambient temp about 45F. It cold idled quite high at 1500RPM, but eventually settled down to 1000RPM when warm at 180F. I screwed in the idle screw about 2/3rds until I got 800RPM warm idle.
I let the car sit overnight, and started it this morning, ambient temp around 40F. It cold idled at 900RPM. (I didn’t have time to see where it ended up when warm, but I would assume 800RPM again)
What is happening? I thought the idle screw makes no difference when cold, or can it? I double checked, and my throttle’s are exactly at .002, and throttle linkage is perfect. So is TPS, and everything else.
I’m starting to suspect a vacuum leak, but it could be intermittent? I will have time tonight to test blocking AAV outlet to air cleaner and go from there. I just wanted to know if idle screw can actually make a difference when cold. Thanks
So I’ve been getting good cold idles at 900 RPM with my rebuilt AAV installed and warm idle adjusted properly.
As a test this morning, I turned back out the idle screw quite a lot. Started her up cold. Sure enough, the cold idle was high at 1300RPM.
Stopped the engine, turned the idle screw in back to where it was for a proper warm idle. Started her up (still cold). The cold idle was back at 900 RPM.
So maybe some AAVs, the idle screw DOES make a difference at cold idle. FYI, mine is from a US spec 1988 Lucas 5.3. It is not supposed to be fully closed until about 175F/80C.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
The idle screw ALWAYS makes a difference at cold idle. The idle screw air passageway is in parallel to the AAV’s piston passageway. It seems to be working perfectly for you. What are you complaining about?
It sounds to me like you are saying you are not getting a “fast” cold idle? Your Cold idle is the same as you hot idle? So the AAV is not giving the expected result?
The idle screw should be used to set the hot idle. Yes it affects cold idle too, but that’s not what it’s for. The AAV admits more air when cold and thus you get a faster cold idle. I guess you could say the cold idle speed is controlled by how far the AAV opens. I am not aware that it’s adjustable, you gets what you gets. Usually 1300ish on my car.
Bob
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
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Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
8
So this thread will probably evolve into a PCV one. Just curious again, as I’m here to learn.
My AAV is working correctly. Once warm at 180F+ I set my idle screw to achieve 750RPM.
I pulled B bank air cleaner (with air temp sensor still connected), and plugged hole to AAV, as well as vacuum line to distributor. My idle only dropped to 600RPM. My throttle plates and throttle linkages are definitely adjusted right.
I suspected vacuum leak, checked everything. Finally pulled vacuum rail that supplies vacuum to PCV system and plugged it, rpm fell to almost stalling at 300RPM.
Is it supposed to pull this much air from the crankcase? Or does this mean I have a leak in the crankcase?
I am using my original OEM pcv that I cleaned a few months ago. Checked it today, still rattles fine, not stuck.
I had to dig up in the archives to find that vacuum line to the PCV
(the 6.0L V12 doesn’t have it)
600 rpm with the AAV blocked sounds off. 300 rpm is about what I get when I do the same with my AAV – different part number btw.
Something doesn’t add up. Hopefully someone that has your engine can confirm.
For the record – on my 6.0L, when plug the AAV port in the B-bank air-filter housing, most of the air that keeps the engine (barely) running comes from the dizzy purge line. One can actually hear the hissing from the little filter.
The pcv would have to allow some air at idle, otherwise it would be stuck closed and there would be no crankcase ventilation.
Maybe mine is opening too much? Perhaps I need a new pcv.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
12
You’re just lookin’ for trouble, aren’t ya?
It does sound as though the PCV valve isn’t working as it should. I dunno how to check it, though, unless someone else here is willing to perform the same test on their car. It’s possible that your PCV valve is working fine and your problem is that your butterflies are too open.
Greg,
I agree with Kirby on this. Your butterflies might be allowing in too much air even though you set them to spec. I had an idle problem once that sounds a lot like what you are experiencing even though I set both butterflies for what I thought was precisely 0.002 inches per the ROM.
Then I adjusted both butterflies to less than that by one flat of the adjustment bolt at a time. I marked each bolt with a dab of paint first to keep track of these fine adjustments. After a couple of adjustments the idle problem was gone. If you mark the adjustment bolts before you start adjusting the butterflies you can always return them to the original position. I think it is worth a try before you start working on the PCV valve.
That’s why I love this forum, the collective knowledge and advice is top notch.
So I was just told butterfly gaps should be adjusted at top, not bottom. (Thanks Dave!). I have been adjusting .002 at bottom, not thinking there was a difference. When I checked at top, lo and behold, A bank was .003 and B bank was .004. So I readjusted to .002 measuring at TOP. The B bank change was enough that I had to readjust throttle linkage.
Got car warmed up, set rpm idle to 750, plugged AAV and vacuum to distributor, idle fell to a stumbling 400rpm.
Got everything hooked up, made sure TPS was still at .32V, set idle in park to 750rpm, and readjusted ECU closed loop mixture (it was now a few clicks too rich, so I readjusted)
I only test drove it 20 minutes, but I think my idle has really smoothed out. The random misfire is 90% gone!
And of course, now I have a strong cold idle with my rebuilt AAV (thanks Jonas!)
Gap should be .002 top AND Bottom. This means your flap is not centered. You should slacken 2 center bolts and fully close butterfly flap so it centers itself and then retighten those 2 bolts that hold flap on the shaft. Also shafts should have rubber seals at each end (C432651 - Throttle spindle seal) If they are rock-hard or missing you might have slight vacuum leak there as well.
No 11 in diagram below:
Greg, search this and the v12 forums. I suspect replacing those seals has been covered.
I know the shaft bushings have been covered well.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
19
Dunno what procedure you’re using, but you’re supposed to turn the stop screw completely away from the lever, insert the .002" feeler gauge and let the butterfly close on it, and tug on it gently so that the butterfly grips it. Then adjust the screw just until the butterfly releases its grip on the feeler gauge. That will only work on one side of that butterfly, as on the other side tugging on it will just pull it right out.
