my dad's 1990 2.9 automatic granada has got a problem that i'm hoping somebody on here can advise on. basically it has an erratic tickover but also when running along at low revs/waiting in traffic it surges/hesitates.

He's changed the TPS (to a second hand one so may still be this...?) and he's changed the idle control valve. he's cleaned out the air intake using carb cleaner too i think. Any other ideas what could be the problem?

thanks