Do you need to remove them and send them for testing or is there atest that can be done at home. I have a stumble at constant revs (say cruising at 70mph on the motorway) A leaking injector may cause this?

Thanks in advance

Ian

O.K. I'm an Idiot. How do you get the air bleed valves (needle valves?) out so you can clean the air bleed ckt.? I've broken one of the little yellow caps trying to fugure out how to get them out. I'm trying to perform a procedure that Ian mentioned for smoother idling when engine how.
Thanks.

If you are attempting to remove the caps on the air balance screws, the only way to remove the caps is to break them.
They are tamper resistant caps.
You will need to buy new caps.
Have you used a vacuum gauge to determine if the throttle bodies are unbalanced?
Once you go down the road of adjusting the balance screws you will want a gas analyzer to check the CO at each cylinder. That is what the ports(bolts) are for on the header.
Good Luck...
Poor Idle!!
Is your engine running closed loop at idle?
Have you set the open loop idle speed?
Have you replaced your plugs within 15K miles?
Have you tested your injuctors to make sure none of them leak and that they have reasonabily balanced. flow.