got a dw8 engine , recently the alternator fried its self and i fitted a new one

pretty sure my idle is reversed since then - when i first start it it idles at 900 rpm and when warm it goes to 1100 rpm and it used to do the opposite

where do i look to fix this - likely to be the wax stat (does this engine have one ? - all my spannering experiance has been done on a 2.5TD land rover 90 ) or a relay somewhere ? or did the alternator damage the ECU - it did take out some other bulbs on the way out as the voltage regulator was what died

thanks in advance