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HOMESERVICE MANUALSPONTIAC1987FIREBIRD FORMULA, 5.0 H, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEM1987-88 COMPUTERIZED ENGINE CONTROLSCHART C2C - IDLE AIR CONTROLDIAGNOSTIC AIDS
1987 Pontiac Firebird Formula, 5.0 H, Automatic

Diagnostic Aids

1987 Pontiac Firebird Formula, 5.0 H, AutomaticSECTION Diagnostic Aids

A slow unstable idle may be caused by a system problem that cannot be overcome by the IAC. The "SCAN" tester counts will be above 60 counts, if too low, and "0" counts, if too high.

If idle is too high, stop engine. Turn ignition on and ground diagnostic cable. Wait 30 seconds for IAC to seat then disconnect IAC. Unground diagnostic terminal and start engine. If idle speed is above 450 rpm in drive, locate and correct vacuum leak. If rpm is less than 450 rpm, adjust minimum idle speed or correct other conditions, which may affect idle.

  • Idle speed may be too high or too low. Engine speed may vary up and down, disconnecting IAC does not help. This may set Code 44. A "SCAN" tester and/or voltmeter will read an oxygen sensor output less than .3 volts. Check for low regulated fuel pressure or water in fuel. A lean exhaust, with an oxygen sensor output fixed above .8 volts, will be a contaminated sensor. This may also set Code 45.
  • Idle speed too low. If "SCAN" tester counts are above 80, system obviously rich and may exhibit Black smoke from the exhaust. The "SCAN" tester and/or voltmeter will read an oxygen sensor signal fixed above .8 volts. Check for high fuel pressure and/or injector leaking or sticking.
  • Remove IAC and inspect bore for foreign material or evidence of IAC valve dragging in the bore.
Fig 1: Flow Chart C2C, Idle Air Control (IAC)
G7122
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.