Holden Commodore 1999 Problems

I assume it’s a V6 auto base model and depending on the condition and mileage done it’s worth between $1400 and $3200.

It's unlikely. It could simply be the doors moving on the seals and rubbing against the body. Put some lubricant on the door seals and see if the noise goes away. If you think it might be coming from inside the door you could also take off the door trim and lubricate the window runners.

The 7-seater can be done, but the ability to fold away the rear seat is lost. The other problem is where to locate the spare wheel, as the LPG tank is located in the spare wheel well. It’s possible you could use a space-saver spare, or a can of foam for emergencies. The best thing to do is to consult an LPG installer and get their advice.

You're certainly doing enough kilometres to justify switching to LPG, but you need to establish the health of your engine before committing. It has already done over 200,000 km, and while the 3.8-  litre V6 is a pretty tough old nail you have to think its best is behind it. At the rate you travel it will have done more than 350,000 km within the next two years, and that's a lot. I would be reluctant to convert it because of is age and kays done, but if the engine is in good shape it could be worthwhile.

The price range quoted by the trade is $6500-$8500, but that assumes normal use and many more kays than your car has done. Yours should be worth more than that, but it’s hard to say how much. In my view the VT II is not yet a valued classic, more an old used car, so there’s not yet the demand for it from the classic car market. But anyone wanting to get in on the ground floor and buy a classic to put aside until the market comes around would be well to pay a little over the odds now. Yours could be worth up to $12,000 to the right person.

The idle mixture would appear to be incorrect. Check first for any possible vacuum leaks that might cause it to be lean and unstable at idle, also check the oxygen sensors and makes sure they are working correctly.