S90 Tickover problem

I've just replaced the head gasket of my S90 B6304S, it is not the first time Ive replaced a head gasket as I am a mechanic but it is the first time Ive done a B6304S, and it's my car too The problem I've got is that although the engine was rebuilt very methodicaly with every bolt going back exactly where it was removed from (except new head bolts, timing belt kit, Gasket kit were bought) it doesn't want to tick over smoothly, it fast idles very smooth but it is very erratic on tick over cams realigned as they were when the engine was being stripped down, timing belt was checked very carefully & every wire, pipe and hose were checked & double checked well before the key was put in the ignition NO fault lights are on, it drives very smooth but the thing just doesn't want to idle smoothly any ideas as Im scratching my head here, Ive done loads of B200's B230's but this is the first B6304S Ive done... & probably the last

Hi, Not sure if there is an idle sensor (there's ruddy dozens of damn sensors!!) but that would be the first place to look.. Check all wires and EARTHS for the engine. I would clean all earth contacts JIC. Des. . . ;)

An erratic (as opposed to surging) idle is usually caused by an air/vacuum leak? I think thats what I'd be checking for first. (I don't want to teach you to suck eggs! :) ). I haven't worked on a B6304S for years so can't say (remember!) anything about specific sensors though I'm afraid.

I've checked all the senosrs.... there seems to be 100's, (LoL) but the erratic idling does give off a sucking or hissing sound but ALL the hose & pipes have had new hose clips on them, then removed and refitted, it is smooth on fast idle (2000-2500rpm) & drives quite smooth, I thimk if I can't find the fault by wednesday Im going to have to take it to the rolling road centre & get it plugged in to a the BIG diagnostics computer he's got

well, well, well..... Who'd have thought that the timing was HALF a tooth out on the right hand cam! I didn't realise that the B6302S was so darn sensative, easily sorted though because the 3 bolts that hold the pulleys on the end of the cams are slotted & not 'key-wayed', with 1 tooth adjustment from one side of the slot to the other I didn't notice they were slotted when I stripped the engine down as you don't need to remove the pulleys and with them set in the center of the slots the flanged 10mm bolt covers the entire hole, she's now running as sweet as the day she was born :Banane32: :a1: :whoohoo: :car-smiley-031: