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

uid 55's pic
posted by  john sargent on  Sat Oct 9 06:31 CST 2004
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last visit: Wed Oct 22 09:07 CST 2014
[RELATED]

Abe's original message is not in the archives, but I will post it here. All credit goes to Abe.

"A 1988 has a three wire idle valve where the center wire is powered via the fuel system relay and the two outer terminals are alternately grounded for a varying duration by the fuel control module. One terminal, when grounded, closes the valve and the other wire opens the valve. The percentages are reciprocals, i.e., if more air is needed to get idle higher the percentage of time grounded will decrease to 42% while the opening signal goes to 58%. High idle can be due to open or unplugged coolant temperature sensor, but this usually gives a rich mixture and poor running if this fault is causing high idle."

"A poor connection on the closing signal wire at idle valve could give high idle without poor running."

"If the wire connectors from the throttle switch and idle valve were disconnected at the same time it is possible to exchange them and end up with the connectors plugged to the wrong items. This can cause high idle."

"Unplugging the idle valve conector with it running on the car doesn't change the idle speed usually as that version of idle valve will simply stop at some opening and stay fixed at that position giving you an idle speed of between 700 and 2000 RPM."
--
john






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