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IAC Valve: Does it operate only at Fully-Open & Fully-Closed modes, or are there different positions ? 700 1985

uid 18083's pic
posted by  lucid on  Mon Sep 20 12:44 CST 2004
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last visit: Fri Oct 24 12:31 CST 2014
[RELATED]

During normal operation, does the IAC valve have just 2 positions: Fully-Open or Fully-Closed ?
It pulses rapidly between open and closed. The average open time (nominally 50%) determines idle speed, with increases for cold running, AC on, etc. as needed.

How is the White/Red test lead supposed to work ?
It should cause the IAC to go fully closed, to allow throttle stop to be set for barely running. This is all described in the 700/900 FAQ. Your throttle stop may not be adjusted correctly if you didn't do the complete adjustment sequence.

On 240 LH 2.2, that test lead comes from the WOT signal input on the ECU. With the TPS set correctly, the ECU then sees both "Idle" and WOT, which I assume is interpreted as a diagnostic call to shut the IAC. If your test lead does nothing, suspect the TPS, it's adjustment, or wiring.

Did you remember to connect the TPS harness? I left mine off once and got similar high idle symptoms.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.






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