Vectra C estate 2003 2.0 dti.

When motorway driving I keep getting the spannner light showing. This only happens when I need to slightly accelerate to negotiate an incline or overtake. Engine doesn't go into limp mode and turning off then on the ignition clears the light.

I have had the fault code read and below is listed the results.

P0638 Throttle Present
( 5A ) Control circuit
Negative
Deviation.

After researching on this forum I have removed and thoroughly cleaned out the Throttle Butterfly Assembly.

I have replaced
ALL the vacuum pipes with silicone piping and checked the boost pipes for splits.

However the problem remains.

Does anyone have any suggestions as to what to look for next?
Many thanks in advance.