Boosted Falcon

Hey, I have a 93 i6 Fairmont auto.
its a clean car, has decent paint with just a cat back exhaust and a upgraded snorkel.
there are a few problems with the way it runs though.
its dual fuel and runs better on gas but when running on petrol it surges (as if someone was playing with the timing) under full throttle on petrol it seems to go alright but still feels sluggish.
when at a stand still and putting your foot the the floor the revs jump to about 1100rpm then SLOWLY creep to 1900 on. the only time it has power is if you drop it down the gears and keep the revs up.
the plugs, leads, dizzy cap and button, coil, air and fuel filter have all been changed with no difference whatso ever.
my brother has a el falcon and we tried swapping ECU's but had no difference.
it was a beefy burble on DE-throttle between 2500-2000rmp but no burble on gas. the oxygen sensor was replaced but made no difference.
sorry about the story I just want to try and fix this problem.
Thanks all, Steve.

welcome, my gfs car does the same thing, when its on gas its fine, but petrol jerks a bit, but the gas place said she needs to get gas spark plugs, and some good gas leads to stop it :S, idk if itll help but correct me if wrong

as far as i know he has the correct plugs and leads...

sounds like it could be a headgasket, take it to a mechanics and get them to do a test.

cheers corey