1994 Toyota Pickup high hc on smog test failure

1994 TOYOTA PICKUP
174,000 MILES • 4 CYL • 2WD • MANUAL
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PTURN
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This is the second time it failed for the same reason. HC max 60 PPM measured 74 PPM. First time fixed by adjusting the air intake adjustment screw. That was 4 or 5 years ago and it has passed smog a couple times since then. Will the adjustment screw fix the problem again or should I be looking for another or bigger problem. If this will fix the problem where should the adjustment screw be adjusted to?
Aug 24, 2009 at 9:21 AM
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RASMATAZ
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Hydrocarbon failures mean unburned gasoline is passing through the engine and entering the exhaust. The three most common causes include ignition misfire, lean misfire and low compression (typically a burned exhaust valve). Ignition misfire can be caused by worn or fouled spark plugs, bad plug wires or a weak coil. Lean misfire results where there is too much air and not enough fuel, so check for vacuum leaks, dirty injectors or a fuel delivery problem. In addition to these, hydrocarbon failures can also be caused by oil burning due to worn valve guides, valve guide seals and/or rings
Aug 24, 2009 at 9:28 AM
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