The Tower is the Base Idle Mixture adjustment. The EHA is used in conjunction with IACV to maintain a Stoic Mixture throughout the rev range. It only goes so far though and if enriched a hair will actually enrich at WOT more, but if you go to far then it can not lean enough to maintain Stoic Mix any longer.

You can see what is going on by having someone hold a VOM on the O2 wire while flooring it to see if mixture stays rich as the rev's go to redline.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....