Removed the pre-cat yesterday on my astra (51), let it run after i refitted it then gave it a clear out down the road. Clear out some oil residue from the pipe. All was fine. Then later that evening driving home i stop at some traffic lights, didnt gun it, as the idle came down to rest all was well for a second then it started running lumpy, not miss firing, lumpy as in cam timing or over fueling, then it cleared it self dunno.. Its done it twice since then, no eml so i havent bothered with diag as yet. Is it a case of the ecu needing to learn again or could it be something else?