Lude Generation

this might seem a little odd, car stood for 3 months (almost 3) battery dead, charged battery and started lude. all ok then after around 1 min of running the revs started changing - would run @ around 1200rpm then rise to 1800rpm hold there for 2-3 seconds then go back to 1200rpm and then repeat the same thing over and over. the ecu had been disconected most of the day, is this part of the ecu relearn procedure? or is something stuck somewhere?
i would just take it for a drive but there is no mot or tax on the car

FITV (when cold) or IACV (when warm) would be the most likley culprits IMO. Is it trowing any CEL codes?

Also, is the coolant topped up?

no codes, havnt checked coolant but it was fine when parked up, i also ran it around 7 weeks ago and it was fine, no bars on the fuel guage though oops. but if it was empty then it wouldnt run at all. also found that during this odd revs business it tries to stall if i try to depress the throttle, switch off ignition and restart and its fine again till i try and move it again, then rev busness starts all over again. maybe i should just risk it and fuel up and drive it up and down the road with no tax or mot but my insurance would be invalid

Is it boucing when the engine is warming up, once the engine has warmed up, or all the time?

dont know, it didnt get to normal temp, wasnt running long enough (no bars on fuel guage ) it got half way then i packed up for the night, will try again this morning - upto normal temp and see what happends or it runs out of fuel

ok just tried again, dont bother replying, think its out of fuel started fine, then after 30 sec or so was trying to stall.

Would that induce a bouncing idle though?

Was going to suggest removing the IACV and give it a good blast with carb cleaner and make sure the valve isn't seizing, then move on to the FITV if it's still doing it, but yeah, you may want to fill up first Still wouldn't have thought it would make your idle bounce like that

When was the last time the fuel filter was replaced? Maybe get some injection cleaner in the tank too?

the car sit sitting on a slope, i think there is air getting sucked up the fuel pump, @ start up the fuel system perges itself and it runs ok, then it takes more air bubles and hey prestow trying to stall, this lowers the demand for fuel and then it has the chance to refill it self again. well this is what im telling myself as i dont want it to be anything else this approach is working so far.