same as me mate, had it to a few places and coming up with about 4 different error codes, they couldnt say exactly what it was, ran this wire from dash to ECU and all problems fixed :)

i have exactly the same proble,, not been able to sort it for six months now. Been to four garages and they couldn't work out what the problem was and have finally booked it in at vauxhall to see if they can fix it.

LOL! Thanks Corsa808 - very comprehensive!
Ian - Yep it's a 94 and the speedo starts at 10mph so am I right to assume that it's cable driven?
If this is the case then I'm looking at replacing the cable to solve it, but if this doesn't work is there an outside possibility that it might be the internals of the speedo clock itself?
Just so I know what to expect.

Cheers for the help people!
:thumbs:

the ecu requires a speed signal from the vehicle speed sensor in the back of the clocks. the ecu uses the vss when engine is coasting to determine the correct position of the idle control valve. the vss sends a pulse signal to the ecu, depending on how fast ypu are going, i.e faster = more pulses per second. the vss is driven directly by the speedo mechanism, so any fluctuations in the reading or a faulty cable can cause a faulty pulse signal to be sent to the ecu, so if the ecu has no signal or a faulty signal, it wont idle correctly. :)

will be as said above bacause th speedo isnt working, ecu picks up a feed to check the speed, if it cant it will keep cutting out. I had this problem when i fitted my digidash as the wire that should have been between the dash and ecu wasnt there. Did paperclip test gave me loads of different codes even took it to a garage and they didnt have a clue what was up with it :o

Its a 94 - cable driven - starts at 10mph?

Sounds like the cable has snapped. ECU light and poor running are directly related to this.

I remeber something about if the speedo doesn't work, the car doesn't run correctly, as it picks up something through the same sensor the speedo does? I believe this is right.

('94 GSi C16XE)
An eventful journey home from work, everything was going fine, 70mph along the duel carriageway when the ECU light comes on (and stays on), car still drives fine and doesn't seem any different - the only thing I notice is that the speedo has now stopped working (:boggle:)
So I carry on my way being a bit cautious incase it all goes pear shaped, have to stop at a few junctions and no problem.
Goto Tescos for a bit of shopping (so car sits for about 30 mins), get in, starts up fine, ECU light has gone off, speedo still not working, first junction I get to it stalls, start it up again and we're away (ECU light is back on), get it home and it wants to stall at every junctions so I have to do a bit of nifty toe/heel to keep it running when I want to slow down or stop.
I get home and park it up, leave it a few hours, go out and start it and it starts fine, idles fine and the ECU light stays off - I've had a few to drink so didn't want to take it anywhere but will go for a drive in it later to see what it's doing this time.

Any ideas?
I'm guessing that the speedo stopping is just one hell of a co-incidence as I believe that they are cable driven rather then using an electronic sensor - can anyone confirm this?
But the more worrying part is obviously the refusal of it to idle (sometimes) and the ECU light being on, I'll do a paperclip test tomorrow but wondered if anyone has had this before and what it could be?

Fire away!
:thumbs: