Ford TSB 89-24-04 IAC diode document with air by-pass valve diag…

TSB 89-24-04 Replacement IAC Inoperative or Rough Idle
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Ford:
Escort, EXP, Thunderbird 1983-88
Mustang 1984-88
Crown Victoria, Taurus 1986-88
Tempo 1988
Lincoln/Mercury:
LN7 1983
Lynx 1983-86
Cougar 1983-88
Capri 1984-86
Continental, Grand Marquis, Mark VII, Sable, Town Car 1986-88
Topaz 1988
Merkur:
XR4TI 1985-88
Scorpio 1988
Light Truck:
Bronco, F150, F250 Ranger 1985-88
Aerostar, BroncoII, Econoline 1986-88
F350 1987-88
F SuperDuty 1988

ISSUE: A rough idle created when the air bypass valve (idle air control) is replaced may be caused by a revision made to the valve's wiring harness. Vehicles built before the 1989 model year had a diode in the air bypass valve's wiring harness. The new replacement valves have a "D" marking on the plastic portion of the solenoid, above the connector cap, Figure 1. They have a diode in the air bypass valve. On the air bypass valve used on vehicles built before the 1989 model year, the positive and negative leads are not important to the valve's operation. However, the polarity on the new replacement air bypass valve is important because, if the wiring harness is reversed, the valve will not work.

ACTION: Reverse the wires in the air bypass valve connector and retest the valve. Refer to the EFI Engine Application Chart for engines using these air bypass valves.

OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: INFORMATION ONLY
OASIS CODES: 620800

See also:
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For other TSBs, check here.

Owner caption September 2014 · Photo 0 of 5000