i have a flat spot on my st170 and was told that it was down to the ecu for the lpg system needing a software upgrade.i went to get it done last week and they told me that the flat spot between 2 and 3000rpm was being caused by a fault with the plenum chamber.they werent sure wether it was down to a relay/control module or the flaps in the chamber.has anybody else come across this?i just need to know wether to try and source a new chamber or not.they cleared the faults but came back an hour later