Yep there sure are other possibilites but the relays would be a good thing to try first..they're not expensive, about a tenner each and are known to cause running issues..even if they don't cure the prob it's a good one to tick off the list anyway.
The other well known thing is to clean the throttle body internal.. another one is the breather pipes coming off the top left hand side of the engine, these can get gunked up..remove, clean through..The plastic section at the bottom though is a bit weak, can break up if not careful..
I replaced the whole pipe arrangement as a general service practice but it's a bit pricey for what it is.
Also check for air leaks/cracks in pipework and the smaller vacuum pipes.
Sorry if going over old ground, i just assumed to your postage count and 'out of ideas' that you probably done all these i've mentioned..
Hope it helps anyway
