Vac problem

[skibumexicano]

Hey everyone..I have a 92 GSX...Sometimes at idle my vac will be between 20 and 18..Which is the correct reading from my understanding?! But other times it will be really low..Between 14 and 16? Somtimes it's good and sometimes it isn't..It really seems to vary upon idle..I don't have idle surge..but my idle is very inconsistent...somtimes it will be between 750 and 850 and other times between 1,000 and 2,000 and holds..I pulled out the Idle air sensor out and cleaned it..It wasn't bad at all...my TPS voltage is running within spec to!! I checked for vac leaks about 2 or 3 weeks ago..My Upper IC pipe was leaking...fix it...then my injector insulators were...Fixed that...I haven't seen any changes in vac or boost..with fixing those leaks..I would really appreciate anyones input on this..It is driving me nuts!! thanks...dan

 

[Lordpaxin]

Check your throttle plate.
your throttle cable

sounds like your cable is a hair tite or dragging on the insulation for the wires looped ontop of your intake.

when its idle is above normal, try to press the plate closed.

 

[skibumexicano]

I beleive i've checked that...The Throttle cable was actually to loose...I tightened it up...But what's weird..my vac is good then bad...It's driving me nuts...Like today..my vac was a perfect 19/20 all day...But yesterday it sucked...thanks for your input

 

[Lordpaxin]

hmmm
is the low vac always associated with High idle

mabye your BOV is intermittantly leaking at idle

 

[crankbender]

the BOV leaking would not significantly effect idle vacume. Also a leak at the TB shouldn't effect it much. Go outside to your car and push on the gas to bring the RPMs up to 2k...you will still pull the idle vacume because you arn't requiring a significantly larger percentage of power to sustain the RPMs. In fact it should remain quite low (-17 in+) even up to 4k RPMs.

It is more likely that where you have the gauge tapped (or in the nylon line) you have a leak. This would allow the engine to idle at a higher RPM and cause the gauge to read a lower vacume.