Mazda 3 Mysterious engine management fault

In the workshop recently we had a Mazda 3 with an ongoing engine management light coming on . The fault first occurred on a long journey and emergency RAC services were called.

Diagnoses was vague and consisted of a list of items that may be causing the engine light to come on.

We were asked to investigate after a local garage were unable to be sure what was causing the fault  the car ran well and when driven seemed to perform as normal.

Initial investigation using a logical diagnostic approach showed a lean mixture fault p0171 this had been misinterpreted as a possible air mass meter fault. The cause of the fault was quickly traced to an inlet air leak around number one cylinder.

A pressured inlet smoke test was used to find the leak.

With customer approval we stripped out the inlet manifold and found that the manifold gasket on number one cylinder had a section missing.
New gaskets and refitting the manifold restored correct running and mixture control.

Section of manifold gasket missing..

Manifold Gasket Missing

Plastic inlet manifold..

Plastic inlet manifold

View of engine with manifold removed..

View of engine with manifold missing