Revs drop by themselves

[LukeLuke]

Ok so I failed the emissions test due to my 2000 , 1.4 Corolla not being able to hold the revs at 3000

When you rev up to 3000 it shoots past to about 3200/3300

When I try to adjust it back to 3000 the revs just drop all the way down to 1500/1900

Even trying to hold at about 2400 there's some slight fluctuation

 

I've changed the lambda, maf, spark plugs and cleans out the Idle air control valve with no improvement

Any ideas would be appreciated as I don't want to have to scrap this engine.

[oldcodger]

 

Could be an air leak on the inlet manifold etc ?

After spending all that time and money, might be worth asking a decent garage to take a look / run a diagnostic on it  ?