My 96 XJS has developed the habit of cutting off and on over and over while driving after about 15 minutes. It started as anintermittant uncommanded shift change at speed and showed a 0727 code (engine speed sensor).
After my mechanic replaced the sensor it started this off on business. it can happen as often as once every 5-10 seconds. Dies just for an instant then catches again. If it had a distributor I'd say that was the problem.
Has anyone seen this before? My mechanic is about to start playing the replace a random part game.

 

By the way, It's got a six cylinder with about 95K miles.
Sam

 

I would have your mechanic zero in on the intake manifold gasket. I had a problem where it would give me problems like yours, but every 32 seconds at idle.

If he's going to start throwing parts at it, the EGR Valve should be first on the list. This problem showed up at idle AND while driving, eventually stalling out my engine after going through a toll, but I was richly rewarded with a CEL code! This engine is so stingy with those codes. EGR was giving me problems for awhile without any indication.

Are the coils original? Have they ever been changed? QYL coils from Amazon are a great buy and seem to be the only aftermarket, not made in Japan, coils that have lasted. I recommend you swap those out if yours are still original.

Is this an idle only problem, or does anything seem wrong while driving?

 

Vee,
So far it has only happened at speed. Sometimes if I have to slow down below 20 it stops altogether but restarts immediately with the key.
Thanks for the Gaskey and EGR tip. I'll have my mech look at it.
Cheers,
SamK

 

And the coils Sam....which is something you can easily do yourself. Don't let the mechanic buy them for you. You'll have a heart attack if you see the price. Order QYL coils from Amazon. All six for less than $100.

Honestly, I'd swap those out first and see what happens...very common issue. If original, those coils are well past their prime. They should be changed at this point, regardless on whether they solve the problem or not. (Might as well replace the spark plugs while you're there.)