Van goes into limp mode on first turn of the key then clears on second!?

Initially the van would not start on a cold day. Glow plugs checked , battery replaced. No difference.Diagnostic expert changed Air mass sensor then cam shaft sensor before admitting defeat. Another mechanic replaced the crankshaft sensor which now allows me to start the van. However when cold the van goes into Limp mode at the first turn of the ignition. Switch off then on again and it starts fine , runs fine. Service carried out , filters changed etc.Any ideas apart from going to Vauxhall with a mortgage? Van has done 80,000 miles. Cheers

Dave Osborne
February 2012