406 0 to 140 in 0 seconds

Hello, I wonder is anyone has encountered this problem on a 406

When I started my car this morning it refuses to idle, the engine revs dip a
couple of times and then drop to nothing and the engine cut out. Here's the
very odd thing.. when the engine was running, the speedo was jumping from 0
to 140 mph and back to 0 over and over again - even though the car was
standing still.

A few months ago the speedo started to fail intermittently after a long (100
mile or so) journey, but has been ok recently. Could this be related?

Car is a petrol guzzling 1997 406 GLX

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Our 306 1.4l did this a few months ago. One evening it wouldn't start
(but starter would turn), then try again and it did start, but speedo
was going bonkers + the rev counter, clicking from relays and stuff. It
drove for a few meters, lurched and then stopped. Restarting didn't
work. After a while it worked again, for a few more meters at 140mph

Called the AA out who after a short time diagnosed it as a broken earth
lead. Turned out the -ve earth from the battery went to the gearbox and
then onto the chassis. Break was at the crimp on the mounting point
between gearbox and chassis - so engine had earth (hence starter worked)
but chassis earthed equipment (eg. ECU and the rest) didn't. When the
lead moved back to touch the gearbox, it would run/start, when it moved
away again, it would stop. The bonkers speedo reading must be due to
the intermittent connection.

He fixed it with parts he had (£4-£5) and everything's fine again.

Might be your problem.

D