Hey guys,
Over the past few weeks I've been straightening up some odds and ends with my car so this problem has moved up on the "to do" list: The cold start on my '87 V12 doesn't work. If you start it up in the morning and immediately try to set off, as you idle out of the garage it will try to stall and it won't behave initially on the road either. Upon starting the idle is at about 400-500 rpm, but after it warms up idle is about 650-750 rpm. I have added to my daily routine, going out and starting the car about 2 minutes before setting off and everything is ok. I know from experience there is supposed to be a cold start feature that lets the engine idle at about 1000 rpm until it warms up to prevent what I am experiencing, I just don't how it works, and where the problem could be. If anyone could shed some light on this issue it would MUCH appreciated.

Thanks,
Lou

 

Lou, to clarify, the engine *starts* OK, right? If so, you have a cold-running issue, not a cold starting issue.

The high idle for cold running comes from the AAV...Aux Air Valve. They commonly are seized up. Some have luck freeing them off...as an alternative to spending $300-$400 on a new one. Post back if you want details on that.

OTOH, many live without a functioning AAV at all. This usually means increasing the base/hot idle speed an additional 100 RPM or so...which would give a cold idle off about 500-550 rpm....enough to keep the engine running. I ran mine like that for years.

Thee's an outfit in Australia....can't remember the name off hand...selling a little AAV overhaul kit. Sometimes it works, other times it doesn't.

The other thing to consider is the coolant temp sensor. If it gives a skewed reading the ECU might not recognize a cold engine and therefore not enrichen the mixture properly. If you have an ohm meter the sensor can be checked. Or...for only $25 or so it can be replaced. That's not too hateful as guesswork repairs go.

Cheers
DD

 

Yes, the car starts alright.. Its keeping it running initially that is the issue. I would like details on the aux air valve. Where is it located? Is there a way to test it (like boiling a thermostat)?

 

The AAV looks like this:

Aux Air Valve - Jaguar Parts and Land Rover Parts

Left side of engine, way at the rear, roughly below the left rear corner of the left cam cover.

The most popular method of freeing-off the piston is to 1) remove the valve (the rubber elbow is a stinker) and 2) put it in a vise 3) screw a sheet metal screww into the top of the piston and use pliers or slidehammer or whatever you can to pull it free

If you get it free you can polish the sides of the piston and the cylinder.

There's a bulb (just like on your thermostats) at the bottom so yeas, you can check operation in a pan of water

Order a new gasket before you take the valve off. Better order a new rubber elbow, too.

Lots of good reading about AAVs here:

Kirby Palm's Jaguar XJ-S Help Book

By the way, the bolt on the side of the AAV is for adjusting the base idle. If the AAV is stuck, though, adjusting it will have little or no effect


Cheers
DD

 

Thanks Doug! I'll get to work finding that gasket. It looks like real fun getting it in and out too.