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Carrera Throttle Hesitation Repair
By Steve Grosekemper
As the miles stack up on your 84-89 Carrera you may notice a slight hesitation just off idle. These symptoms can be caused by many deficiencies, from dirty injectors to incorrect fuel mixture. One of the
most common failures
is the loss of the fuel rail vacuum source. Vacuum is supplied to the fuel pressure regulator and dampener to help tailor the fuel mixture according to engine load. As load increases and vacuum decreases, fuel pressure and mixture go up.
However, if the lines or connections fail and the vacuum signal is lost, fuel pressure and mixture will remain higher than usual under all conditions. With
the addition of unmetered air at idle a lean condition will occur.(The air leak is unmetered because it enters the engine after the air flow meter, and is not measured) The air leak at idle is a large percentage of the total volume that the engine sees. Under acceleration the air leak becomes an increasingly smaller percentage of the total volume. This causes the engine to experience a rapid change in fuel mixture within a very short period of time, and a subsequent flat spot off idle.(The idle mixture is lean because of the unmetered air leak and off idle is rich due to the missing vacuum signal)
The cause for this vacuum signal loss is usually the failure of the connector at the vacuum dampener. It simply becomes soaked with oil vapor and expands,
losing its seal at the dampener. This connector can be found at the forward right side of the engine above #6 cylinder. Replacement is quite straight forward after the air filter housing has been removed.
The connector at the left side pressure regulator and the throttle body can also fail, but it is much less common.. After the appropriate repairs have been made, the base idle fuel mixture should be reset
and the hesitation should be gone.
GOOD LUCK
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