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.)

 

The AAV is almost certainly stuck in the warmed up position. It can be repaired (search fro Grant Francis' instructions) or buy a new one, but they are expensive.

 

Check the rubber boot connecting the top of the air valve. I had similar symptoms and found a hole had been 'sucked' through the aged and hardened rubber. Replaced that and all is good. Good luck finding a replacement AAV. Pretty rare here in OZ.

 

Here ya go.

AAV rebuild procedure.doc

 

Thanks for the tips and the rebuild doc, guys, though I'm starting to suspect that the problem is deeper than the AAV.

 

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

 

You may be right.

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

 

I'm sure many would like to hear about your work-around !

Cheers
DD

 

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

 

The coolant temp sensor got the boot. The AAV may still be a gremlin, but she starts and stays running now.

Thanks for the input!