Prius starts fine but idles a little rough

Just recently my Prius Taxi with 340,000+Km has developed a little problem,it starts fine but after 20-30 seconds it begins to feel like it's not running properly on all four cylinders,if i go to the exaust pipe it seems like it's spluttering slightly,
Yesterday i changed the plugs,checked air filter and all connections,everything fine,
When i accellerate it feels hesitant but after the car gets up to temp it seems to go away,it only happens when i start it first thing or if it's been left for a few hours,
It's never had the throttle body cleaned and i'm wondering if what i'm describing is a symptom of this?
I appreciate all replies,
Regards.

 

Thanks Richard,
I tried all day Friday trying to get MAF Sensor cleaner and throttle body cleaner in automotive stores here in Ireland...most of them looked at me as if i had ten heads and the people i spoke to on the phone..well the silence said it all!!
Finally got one on Ebay in the UK but don't deliver to Ireland but luckily my wife is in the UK for a few days and the guy shipped it on Sat morning to where she's at....i guess there's more money to be made from selling a new MAF Sensor.

 

Thanks for the replies folks,
I cleaned the TB today but that didn't sort it,i did remove the MAF Sensor and indeed it is covered in a soot like substance,i did get a can of CRC MAF Sensor cleaner on Ebay in the UK which my wife has in her possession and she'll be home tomorrow evening so i'll tackle that on Thurs and if that doesn't work i'll move on to the coils,as i said in my earlier post,i've already changed the plugs so that'll narrow the investigation..lol

 

Hi Patrick,
Air filter OK,yeh i'm hoping that cleaning the MAF Sensor will sort things,it's a little annoying on start up only,once it gets up to temp it runs perfectly,
On a completely different topic Patrick...what size is the transaxle fluid drain plug? i'm doing searches but can't find the relevant thread that i've seen countless times!!

 

Thanks Patrick,
Just found the thread...and 24mm socket for the fill plug,
Cheers.

 

Just an update,
I cleaned the MAF Sensor this morning,the car started ok but soon reverted to it's uneven idle but the hesitating under accelleration has gone,infact i feel that it's more responsive.
In relation to V8Cobrakid's coil problem...was the problem persistant?
In my case it's only on start up,that feeling of misfiring but does go away as soon as the car is up to temp,my only experience of a coil problem was with my wife's previous Focus,it was persistant even after warm up,

Any thoughts/suggestions would be appreciated.
I must add that if i shift into D or R,the feeling of misfiring goes away.

 

Just shortly after i submitted my last post that's exactly what i did,get the injector cleaner so we'll see how that goes,i must add that it's not affecting fuel economy,
So far i've,

Cleaned MAF Sensor,
Cleaned Throttle body,
Changed plugs,
Injector cleaner,
Pulled all my hair out,
Chewed my nails down to the crioch [end]

 

It's performing with absolutely no probs Patrick,as i said in my earlier post,since cleaning MAF Sensor and Throttle body i do feel it's accellerating much better and more responsive,i take it that Chevron Techron is a fuel additive/injector cleaner?I've never seen that product here in Ireland but i'll see how things go with the product i've tossed into the tank!!
Do you think that there could be an issue with one of the coils or would that be a persistant problem?
Thanks in advance.

 

We only have one fuel supplier here that has ethanol in it's unleaded [E5]Maxol
They were the only supplier of E85 but discontinued supplying this at the end of 2010 due to the end of a government subsidy,this would have meant that E85 would have been €0.55 per litre more expensive than unleaded which is at €1.45 per litre [at the moment]so they felt that nobody would buy it and rightly so.