Like others have posted, I would suspect the airflow meter pot. You say thatyou feel the symptom is caused by leaning of the mixture from the EHA, but if it simply doesn't provide proper enrichment when you come off idle, it will be lean. This signal is from the pot. If the deposition has completely worn away from the pot where the wiper sits at idle, enrichment may come too late - or the ECU may simply be ignoring its input any more.
Removing the pot for inspection is very easy - four T-15 screws. Just make certain you first scribe an alignment mark across the top where the pot housing contacts the body - for alignment on reassembly.
Alternatively, pop the pot connector cap and check the voltage on the three pins at idle. I understand it should be 0.7 V measured to ground on pin #2 (center pin).