I have just had a new alternator fitted to my 2.5tdi Superb. This involved changing pulleys, belts and bearings which were worn out at 63500 miles! After 20 miles the engine dropped to a fixed 1100 revs with no throttle response. ENGINE WORKSHOP! appeared, the ESP light came on and the glow plug warning light began to flash. There are no fault codes coming up when the AA tested it.

Any ideas?

Check the fuse box in the engine bay for water ingress or corrosion.

Fixed fast idle is the reversionary (limp home) mode for a failed pedal transducer.

Get the codes read and hope it's not the pump.

rotodiesel.