Instead of playing parts bingo, I'd advise hooking the van up to lexia diagnostics. If the Citroen dealer you visited has already done this and is still advising you to keep changing parts until it's resolved, I'd start looking for a more competent dealer.
Somedays you're the pigeon, Somedays you're the statue.
The ECU software version should be checked for most up-to-date, and if it isn't correct a dealer can download the updates.
The most common cause of erratic idling I know, is poor battery connections; the old crimped lead terminals especially are a source of unreliable current capacity. If you have the newer style lever-clamp terminals with the wires soldered in, you can ignore this one. A good battery is one that's been tested on a battery load tester and passed.
Assuming all plugs are good, look at the coil dwell times on Lexia or Diagbox, they should be very close to each other.
Watch your sensor voltages on the diagnostic, ideal is 5V, you may see 4.9 or so but that's OK.
Don't write off mechanical faults such as a vacuum leak from hardened O-rings where the inlet meets the head.
Throttle body faults on an electric throttle body are usually logged as being out of range for throttle position vs RPM. You can also read the throttle position as a percentage off the pedal movement in your parameter measurements, with the motor off.
As it is probably the Sagem ECU, these are somewhat known for dodgy idle/low speed issues. I don't know what causes it but several companies offer a fix for a few hundred.
Thanks guys, that's what is going to happen, but before the van can be hooked up to the lexia, Citroen suggested changing the parts I have mentioned as they say that any part could cause the vault and may not necessary be the one diagnosed. if it does turn out to be the ECU then the names of companies would be helpful.
The coils have been changed the battery load tested and terminals are of the clamp kind and the plugs are new,
There are several sensors fed by the same 5V reference voltage. Yes, a fault in one can affect the others but the crank sensor is the only one (I think) of the sensor "set" that must be plugged in for the motor to run. You can operate without ovygen sensors, coolant temp, MAP, knock and it will carry on a treat with fault codes but you shouldn't get any effect greater than a safely rich mixture and slightly laggy performance.
Ok thanks Addo, just another question, i was browsing eBay for a potentiometer & one of the sellers mentions that they can turn both ways clockwise and anti clockwise, if I remove it is there a way to test which way it turns or do they all turn the same way? I have to remove it to get the part No: