ok so its 2001 uk spec s2000 i bought it with some body damage and repaired it the vtec was not working the gearbox had a slight wine in it so out with the gearbox got it repaired and then refitted it since has been refitted the engine light has come on my mate plugged it in to his computer and it says random misfire but it does not seem to be missing although when you rev the car and the revs drop back down they go to about 400rpm car goes a bit shakey then come back up to about 600rpm. but turned engine light with the computer and the light only comes back on when you rev the car up to about 6000rpm any ideas what could be causing these isues cheers conor.

 

can anyone help with this?

 

Its not a lot of information to go by, but you could start with the basics and check the spark plugs. Did the code say which cylinder the misfire was? Also has it seen a fresh tank of gas lately? You need to start eliminating possible causes to find the culprit and get a little more information while your at it.