Problem With Afm

[r32_Gts4]

how do i know if my air flow meter is faulty? my revs at idle never stays at the same rpm, its always jumping between 4 and 7.

is this cause of my afm?

[J_Red33]

Afm's are a tricky beast to check, the only way to do it properly is with an oscilloscope, and not too many people have them. In any case if ur idle speed is going up & down ur going to have trouble getting reliable readings, though it should give a uniform wave if the idle variation is constant.

I'd actually start looking for vacuum leaks, because that's more likely. I had an intermittent idle issue on my 33 & it would do just what u are saying. It turned out the vacuum hose to the boost gauge sensor was splitting where it was connected to the plenum & would sometimes leak causing the idle issue.

The problem is when you have a leak is that the engine is then sucking in air that it's not measuring from the afm. The computer gets confused & varies the Idle air controller valve to compensate, which it finds very difficult when there's an air leak it doesn't know about. You should check for leaks mainly between the section on anything between the throttle body and the the intake ports of the head. Vacuum hoses, injector seals, gaskets & that kind of thing, even a small leak in this area will have the biggest effect at idle.

Also remove & clean the IAC valve & the AFM elements with a can of carburettor/Throttle body cleaner (also known as a decarbonising spray) as if either of these are gunked up & dirty it can cause problems too.

Hope this helps u out

[r32_Gts4]

thanks alot for the help, i'll check my vacuum hoses 2morow

[J_Red33]

Not a problem. Let us know how you go.