I'm likely to clean it tomorrow at my mate's and buy a can of Throttle Body cleaner to do the job etc.
 
I can try measure it with a ruler or something then!
I'm also sussing this thread out as I write this :)
 
Thanks for all the info, hoping to get some good results out of the clean & later the SARD intake.
Really don't want this to be a more involved issue like spark plugs or fuel pump etc. :/

I'd be looking for air leaks... Get a cigar and start blowing in to tubes

That makes sense @mister2. I'll update everyone once I get a hold of a SARD intake :)

My stock '90 model Gen2 NA does something similar.
When I first start up after the battery has been disconnected I notice that the idle speed is 300-400 rpm higher than normal, and I have to drive it for about 10 mins before it settles down to idle normally.
 
If you want to avoid that happening, you can get an attachment that is powered by a 9V battery to plug in to the cigarette lighter before you disconnect the battery.
http://www.ebay.com/bhp/memory-saver
 
 

So I asked someone who sources MR2 parts and got this response and diagram. But have no idea what I actually need from it... Can someone please help out?

"Hi Andrew, Sure we can assist with these parts, these are parts we would have to order in new for you, all of these parts are discontinued from toyota however i've contacted my supplier in Japan and they have confirmed they should be able to source most of them, I will be able to give a better indication on availability once I know exactly what you require here is a exploded diagram below this should hopefully look somewhat familiar to you 17881 is the elbow/ S shaped intake pipe you mentioned the air intake box was available in sections or as a complete assembly, the sectional availability is now completely sold out so it would need to be purchased as a complete assembly,
I am not sure if the MAF sensor is included in the complete airbox assembly given the part number is raised above the complete assembly i'd say it isn't (although the price would suggest it should be) however it might be I can order the complete assembly in and if the MAF sensor isn't there but required it can be ordered separately, it appears there is a resonator chamber which attaches to the main air intake and then 3 more resonator chambers and air intake duct pipes which I imagine are pre-air box if you let me know which parts off the diagram you require i'll confirm availability and pricing for you,
Kind Regards
Josh"

Thanks guys! :)

About a $1000? That's obnoxious! Doubt it's worth it. Rather try the SARD if that's the case.

To do a proper OEM intake "restore", you would need every part in the diagram – except for the MAF (22204), which you'd already have, the pipe on the lower right (17752) which is totally unnecessary, and the airbox mounting plate (17851), which I would assume should still exist in your car.
 
The bottom line is: Buying all these bits new will cost at least $1000, or maybe even a bit more. The main airbox alone is almost $650 from Amayama... and for the intake system to work properly, you really should have ALL the resonators and correct pipes. It's a tuned system, and removing any of these bits will spoil that tuning.
 
I'd suggest you get that SARD intake for the moment, then keep scanning yahoo auction in Japan (via Importmonster) until a second-hand OEM setup (hopefully) shows up.  I got mine that way, but I had to wait months to even see one listed.
 
There's a BEAMS equipped SW20 with a SARD intake for sale on Gumtreeright now – and this is how it has been fitted: