S1 RSTurbo... the car was tuned and setup nicely just under a year ago but was left standing for just about all the time since....

About 2 weeks ago stuck a new battery on and turned the key.. fired straight up with no problems
but...

Now when starting it up leaving it to tickover is fine but give it some throttle it coughs before revving up and sometimes backfires as if timing is out... leave it to tick over 20 mins or so and allruns well ????

any ideas why