Problems caused by retro fitted speed limiters? Help

[wexican]

I have a 2002 2.4 90ps minibus which has an aftermarket Siemens speed limiter fitted via the throttle pedal.
Ever since I have had an intermittent loss of power when driving.
Had codes read- and no codes present, changed diesel filter, added petrol etc. etc. etc.
I did notice some brown granules like powder or sand after emptying old filter, not metallic as not reacting to magnet, possible just dirt.
So I have now disconnected and bypassed the limiter loom and bus seems to be driving perfectly, no jerking etc.
I know of at least one other case where a similar limiter caused same problem with lack of power worse than mine.

Has anyone else had any thing like this happen?