any ideas???thnx

sounds like your timing could be out

Sounds like it is having a nervous breakdown. Are there any German cars close by?

this has got nothing to do with ignition timing ,its 1 of 2 things ,check the various vaccum pipes for leaks as they often come loose therefore the engine sucks in more air than it should , if all is ok there then you have a dodgy sensor usually airflow at the air intake or lambda sensor in the exhaust causing the engine management to recieve false information and the revs to fluctuate .

l also agree with answerer 3. A vacuum air leak can cause this.
Also, if u have electronic fuel injection, then there is a screw facing upwards between the air cleaner & the rubber connection to the air intake. The screw is aluminium.
Make a black line across this screw. Count the revolutions exactly, that it takes to remove this screw. Do u find black greasy residue on the needle portion of the screw? If so, clean it off & replace with the same revolutions, to original position.
This ABSOLUTELY stopped the same problem when l had it on a 1.9 SRi engine.

Have the idle stepper motor or MAP sensor looked at mate.

sound like the air sensor,
because it draws more air than needed,
it would then make ratio of the air fuel is incorrect ..
the air makes the
engine over fuel at which point it would raise the revs then cut out because then the mixture is to weak..

sounds like either an air leak or a problem with the mass air flow meter.try cleaning the inlet out with carburettor cleaner..