Bongo Fury

hi there. I have a v6/LPG 1998 bongo. engine has started surging when running on petrol, but absolutely fine on LPG. when I start it up it runs fine for the first 10 mins then starts surging.it idles ok and runs ok on low speed but gets worse when I go over 2000 rpm. hope you can help, thanks in advance.

There is a temperature controlled Bypass Air Control Valve (BAC Valve), this uses the coolant flow to adjust the air intake as the temperature changes.
20-990 in the diagram http://www.lushprojects.com/bongopartsm ... o=.html#17
Recently when I had my engine changed this caused problems, not the ones your having but a drop in rev's almost to stall point, but only when the temperature had risen after 20+ minutes driving. I'm not an engine expert in any sense but this might be having a problem and causing your problems ? Be warned access to this is a real bugger down the back of the engine!