1987 XJ-S V12 (5.3L). After starting, idle is smooth, but once it warms up, idle starts "revving" when in park or neutral. See attached video for the sound.

Extra air valve was removed several years ago due to inability to adjust. Five minute timer is also gone.

Any thoughts on what might be going on here?

Thanks,

John
1987 XJ-S V12
75,000 miles

 

Coupla thoughts.

TPS is out of range, and/or going flaky.
Throttle rod adjustment is a tad off.
V12 Black Goo inside the throttle bodies.
CTS having a moment, OR, the wiring to it.
ECU fuel trim "pot" needs a click or 3 to make the thing happier.

SomE PDF's on some of that, just ask if needed.

 

When playing your video I couldn't get any sound so I can't hear how the engine is behaving.

Cheers
DD

 

sound works for me. I used VLC on my phone.
My guess is a bad or misadjusted TPS, or a AAV adjusted allowing too much air. Idle speeds up until the idle cutoff, fuel is cut until cutoff is disable at low RPM, and the process repeats. Problem and adjustment described in Kirby Palm's book, pages 274 and 275.

 

No got AAV, as stated.

None of mine had AAV.

 

My AAV is long gone.

I did back the idle off to 400 RPM, which seems to have solved the issue for the moment. Time and weather permitting I'll look into what Grant has suggested.

Thanks,

John