Vaccum dips well below 20hg when letting off throttle, what happend?
 

Hey guys, i really need you help here. I few weeks ago, i decided to try to fix me idle problem i was having with the car. What was happening was that during operating temperature, if i rev the car up the car wouldnt hold idle, it would dip will below 1000rpm and try to stall. If i turned on the accessory like the Fans, the car would hold idle after revving it up. Any how i decided to to adjust the TAS screw thats beside the Throttle Cable right near the Manifold. After adjusting that something really wacky happend. I noticed that my Vaccum on my boost gauge was sitting close to 10hg! if i turned the fans on, my vaccuum reading came back down to 20hg. I decided to reset the Factory ECU, upon that my reading finally came down to 20hg during idle with no accessories running. Here is the problem now, when i drive the car in gear and let off the throttle i notice that my Vaccum dips well below 20hg close to 30! and i notice i am not building solid vacuum under boost, i dont feel that build up when going under boost. The car will pull 10 pounds but i dont get that build up. Do i have a vacuum leak? and if so what lines should i check? if not, what is the fix?

ummm, i hate to break this to you.. but when you let off the throttle, seeing below 20 on that guage is normal....

Your wrong. it should come down to 20 hg.

You wrong, it should come down to 20hg. Thanks for the reply.

no im not wrong, when you let of the throttle and you are decellerating it WILL normally drop below 20hg... woudl you like to place a wager on this?

how do you have solid vacuum under boost?

^ I'm with him!! (odds, give me odds :))

not solid vacuum under boost, i feel a strong pull from 20hg right up to 10psi.

Anybody else believe that after letting off throttle the vacuum should come down to 20hg? i am very sure that it should not dip below that. The other thing i would like to have answered is after adjusting the TAS would that have any effect on the Vacuum readings?

20h up till 10 psi? that dont sound right

lol, RZRX7TT... you are not a very bright owner apearently.. On my motors i can pull as far as 30hg vacuum when in gear letting of trottle. Its normal, dont tell people they are wrong when you obviously dont know what your talking about.. mmk thx

lmao....

when you let off the throttle the wheels are pulling the revs up with the throttle closed, creating mucho vaccuumo :)

ok cool, so can someone explain to me why my idle wont hold when revving it up? What can be done to remedy this problem. When the accessory like the fan runs, the car holds idle, when revving it up

RZRX7TT, bossman, you sir need to do some reading.

Idle is when the TB is closed- no pressure on gas pedal.
When you apply any pressure on the gas pedal, enough to move the flapper open even a little bit, thats no longer idle. Idle is the RPM your engine holds when the throtle body is closed, so when your going up the RPM range, thats not idle, thats reving.

What happens, is when the engine is idling, and the throttle body is closed, the rotors spinning pulls the air the engine needs in (just like a NA motor), creating vaccum. as your rev the car, and the turbo's come online and build boost, you are no longer in vaccum, as the turbo's pressurize the intake manifolds (boost).

You should go to www.howstuffworks.com and see how a rotary and turbo's work, because it sounds like you are confused on a few terms.

i hate people who ask questions and have their own answers already :rolleyes:

aight enough with the whole vaccum theory, i aight i learned something in regards to that, but someone still hasnt answered my problem! anybody know why the car wont hold idle without the accessories running like the car fans, when revving the engine at idle.

Idle speed control solenoid? Idle air screw?

What RPMs are you holding when you do idle?

I was hoping to get a word in on the first half of this thread. :p:

Basically your asking why your not getting wet when it is raining outside but it isn't raining right now.

You can't rev the engine at idle. You can rev it FROM an idle, but not while at an idle, make sense?

i think your blue steam solenoid is stuck in the high rev/low idle position causing your car to boost in neutral but not in gear. you should go to the nearest chevy dealer and have them plug their diagnostic tool into your obdvii port to make sure your apex seals are not leaking coolant.

i think you need to go ahead and sell your car.....

newbie, meet mr. search function...(hint, at the top of the forum)

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/fixed-my-idle-problems-backfiring-bucking-more-170731/

be sure to check out the links damian provides, and BOOKMARK those sites.

translation: if it ain't broke don't fix it.

Im gonna be nice and try to make something of his above post :)

Do you mean that your car wont idle UNLESS some kind of an accessory is on? Search for ISC Solenoid, that controls your idle in relation to electronic loads. Might have to replace that.

Or he could just take it off, and adjust the idle from the idle screw.

Thanks Team Stealth for your reply. No arrogant remarks, i appreciate it. Unlike some people on this forum.