A new problem has arisen, I’m wondering if it’s an auxiliary valve problem or something else.We have experienced colder than usual winter weather here in Southern California the last few weeks, night time low temperatures in the low to mid 40s Farenheit. Last weekend, I took the car out for a ride. It started right up as it’s supposed to with a, nice smooth idle since I’d recently installed a new coolant temperature sensor. After a ten mile drive I stopped in to visit someone for several hours. When I returned to the car to start it up, I had to crank it twice to turn over, and for the first few seconds idle was a bit low and rough. I revved it up a bit, put the gear selector in ‘D’, and after driving only a block or so, idle was smooth and normal once again. Anyone have thoughts or comments on this? Thanks
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As the engine warms up the slide gradually closes, Mel, and as engine cools it is supposed to smoothly open - ideally taking a a position that fits the engine temp and need of AAV assistance…
For various reasons mismatching may occur; the engine and AAV cools at different rates, and the AAV slide may be sticking. Also, the AAV is electrically heated to ensure rapid closing of the slide; the AAV is a cold start aid - while driving there is no need for extra air. All this may combine to delay starting if the engine is not fully cold or fully hot…
Admittedly, your 10 mile drive is unlikely to fully heat up the engine, but the long standing should indeed fully cool it - depending on ambient air temp. In short; your experience is not unfamiliar and does not necessary imply a faulty AAV - but you could ‘massage’ the slide to reduce/eliminate hanging…
Not all starting problems relate to the AAV, but the main function of the AAV is to raise cold idle - which yours did not do…so…
Frank
We had cold weather today by Southern California standards, and when I started up the XJ6, I had to keep my foot on the accelerator pedal once running for a minute or two to prevent stalling. Since I had recently replaced the CTS, I’m now leaning to consider perhaps the auxiliary air valve is ‘sticking’ in the lean position. As I described to you last week, after parking for an hour or two I had difficulty starting up the car without stalling and a bit of rough running for a minute or two. If the CTS was the problem, this would not have been a problem since the engine had already run to close to operating temperature only a short time earlier. I’m leaning towards the AAV being the culprit now. If so, where can I find one? SNG is no help here. I had an emission test done on the car several months ago, and it passed with ‘flying colors.’ I noticed shortly thereafter that once the engine was fully warmed to operating temperature, idle in neutral which used to sit between 800 and 900 RPM now sits at 800. I don’t know if that makes any difference, as far as the AAV just thought I’d mention it here. As always, your thoughts are welcomed. Thanks
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The main purpose of the AAV is to increase the cold idle by some 400 rpms, Mel…
…it does this by opening the slide cold and closing it as the engine warms up. The slide is moved by a bimetallic spring, easily felt by moving the slide - it should spring back to the initial position, hot or cold, when released. The usual malfunction is grunge build-up over time, causing the slide to stick - and manipulation/cleaning usually works. In principle, the AAV is not repairable, but it can be dismantled for closer inspection/cleaning by drillingout the rivets - then reassembled using screws and nuts.
The AAV is also electrically heated, by a heating element inside, for rapid closing. You can measure the electric resistance by disconnecting the plug - it should read 33 or 23 ohms (two types may be fitted), indicating the heater coil is intact. However, electric malfunction will only delay the electric closing - it has no other effect on AAV function…
Incidentally; using the gas pedal during cranking is counterproductive - it will delay starting. But without proper AAV function the cold engine may not be able to idle - and if the engine cannot idle, it cannot start…
I didn’t use the gas pedal while cranking, Frank. The engine started on the first try without my foot on the pedal but after running several seconds the idle speed began to drop so I lightly kept my foot on the pedal to maintain idle at 1000 RPM for a minute to warm up the engine, then was able to drive. The fact that I recently changed the CTS coupled with your detailed description now confirms to me the AAV is definitely the culprit here. The good news is last night I found a deal on a used one online with someone I’ve dealt with before. I’ll let you know what happens. Thanks again.
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It may be that the electric heating closed the AAV prematurely, Mel…?
That said; driving off immediately would bypass the AAV function by the same throttle action - and warm up the engine quicker. The Jaguar, like other cars, is designed to drive off immediately after start without any warm-up, of course…
I’ll find out soon enough when the replacement AAV arrives. Seller, who I’ve purchased other items from in the past, confirmed all aspects have been tested and are in order. I’ll post an update once the AAV arrives and I’ve installed it. I’m feeling cautiously optimistic.
Just to emphasize, Mel - testing the AAV in-car is simple, as is sometimes restoring its function…
As an aside; in principle, the AAV ‘closed cold’ fault can be countered by opening the throttle slightly. However, it’s virtually impossible to get it right - and, like a misused manual choke, the engine will baulk…
Baulk and stall. The replacement AAV arrived with yesterday’s postal delivery. I changed the AAV on my other car, a 1986 XJ6 eight years ago with a replacement from the same vendor who sent me yesterday’s unit. My tool drawer still has the T30 driver I purchased eight years ago to replace the faulty AAV back then. Yesterday, I spent more time than I’d care to admit removing the malfunctioning AAV from the '87 car along with the various items blocking easy access: air filter, and air flow meter. When I was done, I decided to wait until this morning to start the car up and drive to a location 12 miles away. The car never made it out of the garage. At least with the other AAV the car was driveable. Now, when I start up the car, engine runs two seconds and dies. I even tried starting it up and revving it before it would stall, but as soon as I released any pressure on the accelerator pedal, engine died. Why do you think this is happening? Vendor who sold me the part is a reputable guy, and I’ve purchased other items from him over the years. He claims he tested the unit before shipping. Might it have been damaged in transit? I dread the prospect of having to remove this unit from the car. As I’m sure you already know, undoing the T30 bolts and two hoses is a task I don’t look forward to having to experience once again. You mentioned the possibility of testing and/or repairing the AAV ‘in-car.’ Could you please elaborate on that? Thanks
Mel R.
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You remove the ‘top’ hose and look at the slide, Mel - engine cold, then hot. If the slide is consistently half open when cold, and closed when hot; it is about functioning as perfectly as it will ever be…
An additional test is to use a small screwdriver to push the slide, hot or cold, to fully open - it should invariably spring back to the initial position. The opening and closing is done by a bimetallic spring which bends when heated. An AAV which complies with testing as described is not in itself the cause of starting problems - and it can be tested the same way, out of the car, with a suitable heat source…
The sole purpose of the AAV is to add air to a cold engine to increase idle - which it does with the moving slide.
I quite agree that removing/replacing the AAV is awkward - which is why I test it in-car before doing it. My main problem was to ensure that the ‘back’ hose remained connected when the AAV was replaced - if it falls off, or that hose is leaking or not connected at the other end; starting/running problems will ensue - but it is not the fault of the AAV.
I don’t know what is happening; if the AAV complies with the tests, the only AAV related inspection is to check if the ‘back’ hose is properly connected. However; the ‘fiddle factor’ dictates that all items/areas touched while working on the AAV are suspects…
Is your throttle blade set to .002" and the throttle bore clean?
I’ve run an XJ6 (and XJ12) with the AAV removed from the car and hoses capped off. Never had a problem keeping the engine running, even on a cold start, until/unless temps neared freezing. And even then all that was required was a bit of nursing with the throttle for a few moments.
Last January, during which time from then till now the car was driven less than 1500 miles, my nephew and I cleaned out the throttle body. The car was running well until just two weeks ago. Several months ago, it passed California smog emission test with flying colors. Frank’s postulation referencing the ‘fiddle factor which dictates that all parts touched while working on the AAV are suspects’ necessitated a return to the garage yesterday afternoon, during which time I removed the AAV once again, inspecting the hose connections. I think I may have found the culprit. While examining the ‘top’ hose which leads from the AAV to the throttle body, I found it hanging loose from the metal bar it’s supposed to be connected to leading to the throttle body. I think it may have come off two days ago while I was reattaching the AFM, which, as you know, is mounted on a metal bracket obstructing the view of the spot where the hose connects to that metal bar leading to the throttle body. I carefully reattached the hose to that metal bar, making sure it was fastened securely. I know it was attached two days ago, but I wonder if it might have come off when I reattached the AFM two days ago. I did not attempt to start up the car yesterday, as I was already running late to a prior commitment, but I’m hoping to try to start it up later today. Do you think the ‘dangling hose’ might indeed have been the cause of the ‘no start’ condition? I’m hoping so, lest I begin to experience nightmares with T30 bolts swirling around my head…
I tried to start up the car today, still idling rough, had to keep my foot on the accelerator to maintain 2000 RPM to prevent stalling. I ran the motor five or six minutes to at least approach operating temperature, and though rough idle smoothed a bit, still would stall if I remove my foot from the pedal. I brought the ‘old defective’ AAV home and placed it in the oven set at 170 F for 15 minutes to warm it up and see what happens. The valve appears to be stuck in the partially open position, so I know at least it is defective, but I don’t know what to do now, unless, heaven forbid, the back hose somehow became disconnected from wherever it leads to from the back of the ‘new’ AAV. Is it even accessible, or must I crawl underneath the car to find it? If that back hose has indeed become detached from wherever it is supposed to be, would that explain the difficulties encountered now?
If detached it would be a vacuum leak, letting air into the engine past the AFM. And opening the throttle may reduce the leak effect - getting the mixture more suited to the engine’s needs. It is certainly a first step as you have been working ‘in the area’ and verification is prudent. It may of course be another issue, though the symptoms are familiar enough - checking throttle gap as Doug says. And indeed; verify that the air duct between AFM and throttle body is fully seated, secured air tight with the clamps and undamaged…
But do check slide reaction, on both AAVs, to forced movement with a screwdriver as described - in addition to the heat/ cooling tests of course. And watching, during heating and cooling, that the slide moves smoothly. The engine heat is transferred to the AAV from the smooth ‘sole’ of the device - place that on the lid of a casserole to heat i…?
I think you now have me closer to finding the cause of this difficulty. Like you suggested, I think there are several issues which came up at the same time. During the weeks preceding me changing the AAV, I noticed the engine idling just below 800 RPM in neutral, which I wondered about since I’ve been used to it idling 850 to 875. This possible aberration was accompanied, as I described earlier, by having to start up the car twice to not stall after driving somewhere 10 miles away and leaving the car parked for an hour or so. This condition is what led me to replace the AAV. The fact that the car could not run more than a few seconds after starting it u with the replacement AAV leads me to believe the lower hose of the AAV may have been detached when I removed the old AAV from the car. So, today I plan opening the throttle body to check its condition and make sure elbow coming from the AFM is properly seated. I’m due for an oil change, so when he has time, I’ll book an appointment to have my mechanic put the car on the lift and check on that AAV hose while changing oil. Hopefully, the mystery will be solved. Does that make sense? Thanks
UPDATE
Good news! Last week I finally received the two hoses which connect to the AAV as well as the accordian shaped rubber hose connected to the back of the air flow meter and throttle body. I had the car towed to my mecanic’s shop today.
Net result? The hose which runs from the back of the AAV had probably torn when I replaced the old defective AAV weeks ago. He installed the new hoses today and cleaned out the throttle body as well. Car now runs better than ever and I couldn’t be more pleased. Thanks to all for your sage advice.
Mel R
