edit: fixed original issues.

Please see #6.

if you are getting the engine light, maybe try shorting pin 1 on the diagnostics plug to see what error you get.

edit: Fixed

Take it back to the LPG installer and leave it there until it is fixed. I had quite a few issues after mine was converted and had it back about 4 times until they got it right. Now, 80,000 klms later, it still runs like a dream. If there were none of these issues prior to the conversion, then it is the installers responsibility to fix it.

To anyone who read my post about my issues, specifically with the engine warning light, I opened my bonnet and found my issue. Very embarrassingly, it looks like when I cleaned my engine bay last week I didn't reconnect my Air Flow Meter! DOH! - How did I not realise and drove the car like that! $40 worth of petrol wasted in less than 150km's. Grrrr exxy mistake!

Anyway I've got a interesting problem with gear changes. Especially on lpg, the car shifts to the 4th gear a little early around 55-58km's and if I back off the accelerator for only a little bit - the rpm's drop quick and the car is not responsive for about 5 seconds. I can put my foot to the floor and nothing happens. I need to wait until the gearbox very roughly downshifts to 3rd and then jerks forward and I'm good to go in 3rd gear. How can I fix this? Currently I'm trying to retrain the box to keep 3rd gen till about 65km's constantly using my shifter. Obviously this isn't a solution for the long term. Any ideas on how to fix?
Could the tps be responsible again?
Or maybe the throttle body is dirty? The car jerks pretty bad if I back off the accelerator at 70kms+, especially if I'm in third gear. I tried to clean my tb the other day, but the mixer blocks all access to the bolts by a socket, so I needed to use the open end of a spanner. All bolts came loose bar one which is now seared :/ The mixer is held on very well by Ultra Blue and I'd want to avoid having to pry it off. May not have any other option at this stage =/
I was thinking of adjusting my SAS screw but I'm a bit reluctant as I don't think its been touched since factory, where it was properly adjusted. It would also mean the car would idle higher on petrol which currently is at the right speed at around 800rpm.
The idle is computer controlled so I can't override it. Could the ISC servo be faulty?

Any ideas?