Vacuum leaks
Vacuum leaks are a common cause of drivability problems on the Pontiac Fiero.
A vacuum leak allows unmetered air to enter the engine, which can affect idle quality, fuel mixture, throttle response, emissions, and ECM control.
Overview
Vacuum leaks can occur in hoses, intake gaskets, vacuum fittings, brake booster lines, EGR components, throttle body gaskets, or other intake-related parts.
Symptoms may differ between the 2.5L four-cylinder engine and the 2.8L V6, but the basic diagnostic approach is similar: inspect for air leaks, damaged hoses, loose fittings, cracked rubber, and intake sealing problems.
Symptoms
Common symptoms of vacuum leaks include:
- High idle
- Rough idle
- Surging idle
- Stalling
- Hesitation
- Lean running
- Poor throttle response
- Hard starting
- Hissing noise
- Poor fuel economy
- Stored Code 35 or Code 44 in some cases
Common leak locations
Possible vacuum leak locations include:
- Vacuum hoses
- Intake manifold gaskets
- Throttle body gasket
- EGR tube
- EGR valve gasket
- Brake booster vacuum line
- MAP sensor vacuum line
- PCV system hoses
- Cruise control vacuum lines
- Vacuum fittings
- Cracked or disconnected rubber elbows
V6 EGR tube leaks
On V6 Fieros, the EGR tube is a common vacuum leak location. A cracked EGR tube can cause high idle, rough idle, lean running, or drivability problems.
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Diagnosis
Vacuum leak diagnosis may include:
- Inspecting all visible vacuum hoses.
- Checking for cracked, brittle, loose, or disconnected hoses.
- Inspecting the EGR tube and EGR gaskets.
- Checking the MAP sensor vacuum line.
- Inspecting the brake booster vacuum line.
- Listening for hissing sounds.
- Using smoke testing if available.
- Watching idle behavior and ECM data where possible.
- Checking for related diagnostic trouble codes.
Smoke testing
A smoke test can help locate leaks that are difficult to find visually. Smoke is introduced into the intake or vacuum system and escaping smoke indicates a leak location.
Care should be taken to avoid damaging sensors or forcing excessive pressure into the system.
Related trouble codes
Vacuum leaks can contribute to several trouble codes, depending on the engine and conditions.
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Repair
Repair depends on the source of the leak. Common repairs include replacing vacuum hoses, replacing gaskets, repairing or replacing the EGR tube, tightening loose fittings, or replacing cracked plastic or rubber components.
Notes
Vacuum leaks should be diagnosed before adjusting idle settings or replacing unrelated parts. A vacuum leak can make the ECM compensate for a problem that is actually mechanical or sealing-related.