Engine diagnosis challenge!

[NDT]

I'd welcome any suggestion on what's making our 2.5T S-Max hesitate at light throttle....

She idles smoothly and the CO is ok at idle.
Pulls like a train at mid/full throttle.
She hesitates slightly at light throttle from 2000-3000rpm - for example if you're in 5th or 6th at a steady 60 or 70mph.
Spark plugs are new
The only work that's been done recently is a new boost control solenoid.
I've cleaned the MAF sensor (made no difference)
There's no dirt on the throttle.

The only fault code that has shown up (checked by a Ford dealer) is PO61A - PCM Torque Performance. Nothing else showed up when they plugged in the diagnostic check.

Any thoughts?

[HustleRussell]

You sure it isn't just the usual flat spot these engines have when the EGR valve opens and coughs a load of particulates into your inlet manifold?

[NDT]

HustleRussell said:

You sure it isn't just the usual flat spot these engines have when the EGR valve opens and coughs a load of particulates into your inlet manifold?

I'm fairly sure this is a new thing - in fact it seemed to have appeared after the boost solenoid was changed.

[Bennachie]

Plug gaps. Too small.

[NDT]

Bennachie said:

Plug gaps. Too small.

Thanks for that - I'll check when we changed the plugs - the problem started when we changed the boost control solenoid (or it was pre-existing and it was hidden by the boost solenoid problem) and I can't remember whether we changed the plugs at the same time or afterwards.

[350Matt]

Air leak post MAF meter

[davepoth]

It could actually be the solenoid doing its job properly - lowering the boost level at light load.

[NDT]

Thanks all.
I'm going to try to track down a post-MAF leak with ether.
I need a code reader too as I'd like to look at lambda while it does it to see what's going on.