88 XJS V12 starts, stalls
#1
88 XJS V12 starts, stalls
Lately I've been having an issue with my car stalling shortly after startup. I can keep her running only if I hold the engine at 1,500 - 2,000 RPM for a minute or two. I suspected the auxiliary air valve, and had a shop confirm my suspicion (though they couldn't duplicate the problem 100% of the time.)
One cool rainy morning I noticed a cloud of smoke or vapor from the exhaust, which faded quickly and I don't recall an odor of fuel. That evening, after work, she behaved the same way but this time without the cloud.
Are there any other culprits I should look into? Once warmed up, she runs just fine. No performance complaints (though I know she needs a tuneup.)
One cool rainy morning I noticed a cloud of smoke or vapor from the exhaust, which faded quickly and I don't recall an odor of fuel. That evening, after work, she behaved the same way but this time without the cloud.
Are there any other culprits I should look into? Once warmed up, she runs just fine. No performance complaints (though I know she needs a tuneup.)
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Stargazer XJS (05-20-2017)
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Someone will correct me if I'm wrong on this, but if the AAV is indeed stuck in the warmed-up position, you can experiment with creating a vacuum leak somewhere to see if that increases the idle speed enough to keep it running. If it does, please say so and I can share my homebrew "cold air start assist" system that works around the problem if you don't want to spend +$300 US for a NOS AAV.
Thanks,
John
1987 XJ-S V12
Thanks,
John
1987 XJ-S V12
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A week's pay says that not one-in-five old V12s have functional AAVs and their owners are not even aware of it.
I have a dead AAV on my present V12, and my previous V12 had a dead AAV as well. Then or now I have no stalling when cold....unless we're talking about ambient temps approaching freezing, in which case a couple throttle goosings might be needed immediately after start-up.
A lot of things can influence cold running, not the least of which is the coolant temp sensor. These are easily checked....or for $25 you can replace it and hope for the best. As guesses go it one of the least painful.
But most any fuel or ignition system weakness can cause problems with cold running. Often cold running problems are a stack-up of minor faults which must be discovered and repaired. It might be said that the high idle provided by the AAV, if yours was working, can mask problems elsewhere.
I'm not saying "Don't fix your AAV" but I agree with your thought that something else might be afoot.
Cheers
DD
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Stargazer XJS (05-23-2017)
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Greg in France (05-24-2017)
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Just hold the throttle open a little; you'd be accomplishing the same thing. I would think 1000-1200 rpm should do the trick.
On the V12s, since incoming air isn't measured in any way, the fuel injection system doesn't 'know' or differentiate if air is coming in via the throttle plates or via a vacuum leak. Air comes in, the engine reacts, and the F.I. responds via the MAP sensor in the ECU.
The AAV is, in essence, just a controlled, timed vacuum leak.
Cheers
DD
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Greg in France (05-24-2017)
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Grant Francis (05-27-2017)