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Jag cutting out

I have a 1984 XJ6 and while driving the RPM dial will go wild and then the car dies. It starts up again no problem. There doesn’t seem to be any pattern to this. The car has a new transmission and I just replaced the starter…any ideas what could be causing the problem?

If the tachometer, correct term for RPM dail, goes wild, but engine doesn’t, I suspect the ignition system. The tachometer gets a signal from the ignition module everytime it signals the coil to fire, and the tach converts that to the dail reading. A wacky tach usually means a wacky ignition system. And, IIRC, Jaguar was using Lucas electrical systems back then, perhaps the worst electrical and electronics supplier in the world. The bulk of the ignition system could be compromised, from the pick-up coil in the distributor to the ignition module to the coil.

Thanks - WHen the mechanic changed the started he wasn’t able to change the coil as the car refused to start. Woudl only start with the old coil. Car starts but it’s up to it’s old tricks again. When I go up hill and excelrate the RPM goes and she dies. Am bring it to a Jag repair shop Friday and am hoping for the best.

Thanks for your help