My 1988 XJS V12 starts sluggish, idling around 350RPM, then after the 45-second ignition retard timer expires, it bumps up to 750RPM and runs fine. As I understand it, the timer is supposed to be opening the supplementary air valve to stabilize the idle during that 45 seconds while the ignition timing vacuum advance is disabled, but something about that setup isn't working.

Anyone have an idea on where to start looking, or how to test? Can I just disable that timer? Where the heck is it?

 

When I bought mine the PO bypassed all the vacuum control system and ran the advance right off of ported vacuum.

I tried returning the system to stock configuration (USA and Australian variations) and never was sure if it was working right. It's a complex system and everything has to operate in the correct sequence, as you know. I gave up and returned to the direct system.

Not much help, I know. I'd bypass the timer and see what happens. You might like the way it runs. The timer is under the dash somewhere...I can't remember, sorry. I'll try to look it up for you.

Cheers
DD

 

I would bet on a jammed closed AAV, and that notorious "gunk" around the 2 throttle discs.

The AAV is well documented for jamming, usually in a partial open position, but I have had 2 jammed solid in the fully closed position.

Remove both air filters, and with a solvent soaked rag, wipe out both throttle bodies, they will be black with this gooey black stuf. Take your time and get them both CLEAN.

 

I replaced the AAV a few years ago since the original was stuck fast. That would cause the idle to increase up to 2000 RPM since it wasn't closing down. This isn't an AAV valve problem, but I'll look into the gunked up throttle bodies.

 

Heya Doug. Yeah, this is what I'd like to try, but I can't seem to locate the timer, or I'm not sure what I'm looking at.

 

The timer should be on the right side component panel below the glove box.

At the timer itself the wires are pink/white, black, slate, white. At connector CP8 behind the dash the slate changes to white/blue and the white changes to brown/slate.

Hopefully this will help you find it

Cheers
DD