I found one on advanced auto parts website.....
http://www.advanceautoparts.com/
Dorman 4-Wire GM Idle Air Control Valve Harness: Conduct-Tite!(R)
Part Number: 85112
For Your Vehicle
Vehicle: 1988 PONTIAC FIREBIRD TRANS AM
Engine: V8 5.0 Liter FI
Idle Air Control Valve Pigtail/Connector:
Retail Price: $25.61
Our Price: $19.99
You Save: $5.62
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This one was on autozone's website
http://www.autozone.com/home.htm
Connector - Idle Air Control Valve Duralast / Connector - Idle Air Control Valve
for a 1988 Pontiac Firebird
Idle Air Control Valve
Part Number: 239
Weight: 0.079 lbs.
Pricing:
$16.99
you can even try
www.rockauto.com or
www.tpiparts.net as well.......