what can cause idle fluctuations?

[Marky]

On SOME older cars the factory valves can leak when you run more than factory psi - early evo comes to mind - and some factory valves are designed to leak slightly at idle / light throttle as it\'s an effective way to "bypass" the turbo at low loads & when it isn\'t needed which helps economy. I\'ve read online the late model valves can leak on boost once you get to upwards of 25psi ish... but that\'s another story.

94 Leone - You\'re better off blocking the factory one off for now rather than leaving it to vent - it\'s not just un-metered air, it\'s also unfiltered getting sucked in as well. Plus you\'ll get some sweet sweet fluttery noises yo

Back to original topic - my current BH was identical when purchased, it actually took me a few days to even notice the idle was bad. Drove fine otherwise, idle just got progressively worse over about 30 seconds. Fault was with the AFM, but I did find idle stepper thing was quite gummed up and found a couple of vacuum leaks in the process of trying to fix the problem too, which would have compounded things.

20 vac on idle is quite normal & healthy in my experience.

[public_nuisance]

20vac is good for most cars, quick easy way to check for vac leaks is to see if 20vac on the gauge at idle

[Stoffa]

20 what?

mine sits an 50cm/hg

[Marky]

Some boost gauges just have -30 to +30psi

I have no idea how the conversion works out haha

[public_nuisance]

-20 psi vacuum is the standard for a "WARM" idle on most turbo cars, well all that i have had, and usually if the cars not running right, and it doesnt have -20 i find there is a vacuum leak. hope this helps.

[scoobygt]

the car seems to have come right haha

[Guest]

Iv got another suby a 1994 legacy wagon gt. its been at my auto electrician for the last 2months. Free of charge because they cant figure out. Replaced pretty much everything. Theyve asked just to leave it with them and to slowly try figure it out. Wtf...

[scoobygt]

maybe it\'s the motor? bad compression or a bad valve