Strange Idle Issue

[trotter]

Been going on for a few months now.

Starting when properly cold, engine catches no problem, revs go up to 2k or so, then immediately come back down to ~1k as always. However, as soon as I press the loud pedal to move the revs drop right down below 1k and she starts to shake as if she\'s not firing properly. Quick stab of the throttle to take the revs back up to 2k again then she settles down fine after that.

Then, while sitting at lights, etc, I hear the occasional \'burp\' from the exhaust which sounds awful like a misfire, looking at injector duty on commander shows no change while it\'s happening.

It\'s not plugs or leads as have just changed both, it got better for a bit then came back.

Could I be looking at a boost leak issue here or is it something altogether more sinister?

cheers in advance

graeme