Ok. so i've been thinking(scary) and i came to wonder...if you increase airflow to your motor(like intake mods or high flow tubing or air filters) would that decrease your vaccum? i took out my maf screen and my rain shields on my intake. the rain shields didn't do much but after taking out the screen i have a very rough idle. could that be do to decreased vaccum in my manifold? just a theory...can anybody make some sense of this?

 

I'm sorry to say it but chances are you messed up your MAF. I'd replace it and see if that makes a difference.

 

I would say no. The motor only pulls what air it needs. lets look at it at idle; the throttle blade is closed. The motor is pulling x amount of air regardless of how much your intake pipes can potentially flow. IF (big IF), you're trying to pull more air at WOT than your intake tubing will flow, by increasing the flow through that section, you may see a very minor change in vaccum. However, being that you typically see 0 vaccuum at WOT, you wont notice any difference on vaccuum. Performance, maybe; vaccum, no.

 

well i didn't touch anything else but the screen. my maf would throw a code if it flat out wasn't working, right? so i'll unplug it and see if that changes the idle. if i messed it up then i don't really care because i noticed a performance gain. idk. just a thought. and i understand that your computer runs a different mixture when you are in open loop i.e. when it's cold. it seems like a have more power then in the low end. maybe i'm running lean in closed loop? input?

 

When an engine is in open loop it dumps the fuel in. The computer ignores all sensor input and runs on a programed air/fuel mixture until it's at operating temp. To get rid of the lean condition in closed loop, give the engine a real good tune up. New oxygen sensor, coolant temp sensor, plugs, wires, dist' cap, rotor, and spray the intake down with a good EFI approved intake cleaner. Advancing the timing 1 or 2 degrees will help with bottom end power as well, but with a loss of high-end speed. As for the vacuum, an N/A engine pulls only as much air as it needs (its called volumetric efficiency). Adding a turbo will reduce engine vacuum because its forcing a positive air charge into a negative air charge space, (remember vacuum is any pressure below atmospheric pressure, 14.7 psi)

 

Yes it will cause a drop in vacuum. And a drop in throttle response if you go too large. Most motors aren't at 0 vac at wot, the stock induction isn't very free flowing. Even worked over motors struggle against induction restriction. Some inductions like a tunnel ram can however develop more than 100% ve naturally aspirated. Anything you do that increases airflow into the motor reduces vacuum in the manifold. If you put a throttle or carb that's too large on response suffers because air has mass. It takes longer for a larger quantity of air to overcome it's own inertia and get moving than less through a smaller tube.

You need to keep the maf screen, it's there to keep crap out of your motor and reduce turbulent airflow. The ecm only ignores the o2 sensor in open loop. Chances are your maf's in very bad shape. It's still functioning, but covered in a layer of crap, or the lamination is separating which won't set a code until it gets really bad (which would probably end up as a lean or rich code instead ). It won't set a maf code unless it's not functioning or it sees a way higher voltage than it should.