AFM test results - can I be sure my AFM is defective?

[Belle427]

The old spray test with carb cleaner or similar may help too to find a vac leak just take care when doing.
Smoke test is obviously better but hardly worth buying one just for this.

[eliot]

blaze_away said:

As a reference check I checked what happens on my engine when I clamp each of the crank case hoses to the plenum.

1. No impact on rpm
2. Moderate decrease in engine rpm
3 Moderate decrease in engine rpm

Concluding that (metered) air is drawn from outside the butterfly to plenum when butterfly is shut and plenum vacuum is at its highest.

Edited by blaze_away on Tuesday 2nd January 20:32

Unmetered air surely - it’s after the air flow meter?
Also, is the water jacket underneath the throttle plate present - it wasn’t fitted on some, it’s important that the bolts are replaced otherwise you get another big air leak under there.

[blaze_away]

eliot said:

Unmetered air surely - it’s after the air flow meter?
Also, is the water jacket underneath the throttle plate present - it wasn’t fitted on some, it’s important that the bolts are replaced otherwise you get another big air leak under there.

Just to clarify....It is metered air as its passing through the MAF, its uncontrolled (to some extent at least) as its just a hose bypassing the throttle butterfly. belle427 oh thread link explains everything very well indeed.