just managed to get the s1 started, if you hold a constant 3000 rpm rev it is fine and firing as should, but as soon as you let it drop below that it seems to miss horribly sound like firing on 2 or 3 cylinders, then cuts out if let off the throttle??

 

try taking the rocker off and checkin every thing..my mates 1strocker was fucked and wouldnt run under 3g but fine above(strange)good luck....iv got take my engie out tomoz

 

Air leak i would almost definitely say.

With an MFI system everything connected into the system is detrimental to the good running of the engine, if anything develops an air leak you will have running problems.

Check hoses intercooler etc for splits/air leaks.

If not try disconnecting the long breather pipe that runs from the rocker cover to the air flap and block the hole in pipe in the air flap box.

Failing that try also disconnecting the brake servo vacuum pipe and once again block the hole into the inlet plenum.