1. Irratic idle when in Drive/Reverse - the idle is fine when in neutral and can be altered up/down without a problem. It seems though that when the car is in Drive/Reverse it doesn't idle so well. It drops down to about 400rpm and is very close to stalling but then (mostly) increases back up to the idle speed after a couple of seconds;
2. The first time we fired it up, we believed it had an airlock in the cooling system. We think that it still may be there or alternatively something else is not quite right. I've been cautious about this motor overheating, as 4.4's tend to do. After going for a drive, a fair bit of water escapes from the expansion pipe and you can still here it bubbling away afterwards. Could it not be an airlock and perhaps something wrong with the radiator? The temperature gauge is sitting under half so it doesn't look like its actually overheating.
3. At the moment it only runs on petrol, but the gas wont work. We can get the tank to switch over to gas but after about 3 seconds it runs out of gas (there is still plenty in the tank).
4. We have one plug left over on the passenger side near the coil. It is similar to an injector plug in appearance but we have no idea wtf it is for. It runs from the coil and is earthed, but doesn't seem to go anywhere. Maybe this mystery plug will solve all my problems?

BTW, its still running the 3.5 injection and airflow meter which may have something to do with it (although i hope not).
TIA.