91 XJS coupe, 5.3L V12, 105K miles,

On starting up my car after its been running for a while (30 minutes +, highway speeds), the idle seems to pulse up an down, and unless I give it gas, it feels like it will stall. Once under way a few moments, engine is running fine again.

Any suggestions what this might be, or where to begin looking? I use only 93 octane gas and had a full tune up maybe six months ago (did it before as well).

Thanks.

 

Well, its a Marelli car, so the rotor mod pops up as usual.

The AAV (auxillary air valve) at the rear of the LH cylinder head is maybe not closing 100%. Very common.

The spark plugs are gapped wrong, common.

The O2 sensor/s are flaky. I read this as common, had no failures on ours with our fuels.

Throttle discs are caked with "goo", and/or set incorrectly. Very common.

CTS (coolant temp sensor) on the LH thermo base is flaky, common enough.

The TPS (throttle position switch) under the throttle capstan at the rear of the engine is going bad, common enough with old age and heat now.

The list goes on, but that will keep you occupied for a few hours, and then we will continue if nothing changes.

 

Jeezas, all of the above, you got me scared as well.

 

Maaaaaate.

All that can be sorted in 4 hours TOPS.

Also, all of that above is part of MY "catch up maintenance" on any V12 s/hand car purchased by anyone that actually wants it right and reliable.

Send it down to the colonies and I will do it for you, mmmmmmmmm.

Take up drinking, things always look better with a stiff JD lubricated the brain cells, HAHA.