IS200JJ

Hey guys, I have a 2001 IS200 manual which has developed this problem over the last couple of months: Starts fine 9/10 times. Drives perfectly once started. 1/10 times it just turns over and won't start (recent new battery with good voltage, turns over fast). If I press the throttle it will try and catch and may struggle to idle very slowly, and very, very lumpy before stalling immediately. The only way I can start the car when this problem occurs is to turn the key, hold the throttle down full and it will idle very roughly at maybe 2-300 rpm spluttering away for maybe 30seconds before the revs slowly climb, and the engine begins to rev throughout the range as normal. I can then release the throttle and it idles and drives as normal. This problem occurs intermittently both when the car is cold, and when the car is hot after being turned off and restarted. Any ideas? I'm thinking it must be either throttle body or ignition (spark plugs / coil packs), but I have little experience with IS200's. Thanks, Jonathan