Vacuum Issue or Slow IAC?

[jmgtp]

I suspect my car to have either a slow IAC or a minor vacuum leak that I'm having difficulty tracking down. All the intake gaskets and most of the vacuum lines are brand new. There is a T connection for vacuum hoses beneath the cruise control unit. One of the lines from this connection leads under the washerfluid tank before it goes out of sight, I didn't bother following it any further but I'm assuming it goes to the vacuum ball. I pulled this line out of the T connector and put a piece of vacuum hose on it. Using lung power I sucked on the line and I could hear it 'inhaling' air or if I blew through the line I could hear air pushing out. It was as if nothing was on the end of the line because there was very little resistance. Is this normal? Or have I found a leak? Seems to me if this was connected to the vacuum ball this line should be air tight, how else could it possible retain vacuum? Does the vacuum ball just have one line running to it or is there more than one?

Note: All vacuum operated devices (hvac, cruise control, etc) function normally. Once the car is at a full stop it take a bit longer than usual to return to idle speed. It hovers around 1200 rpm on the tach for 5 seconds or so then drops to the 1000 mark. I realize this could be tach error, but other times it drops to what appears to be 800-900 rpm and when it does so it sounds more like a lower idle. From traffic light to traffic light it won't hit the 800-900 rpm. Usually it settles somewhere between 1000-1200 rpm but if I let it idle for a minute or two it seems to find its way down to a lower idle.

Thanks

[Anonymous]

The 3.4 will stay at like 1200 until it is COMPLETELY stopped, then it drops to normal(800). The vacuum ball has one line running into it.

[jmgtp]

I'm aware that it hovers a bit before dropping to idle speed but the fact is that mine doesnt drop to idle speed and continually hovers between 1000-1200 rpm, and only achieves true idle rpm if left for a minute or two without touching the throttle. Can anyone verify that the vacuum ball should be 'air tight' if vacuum is applied to the line running to it?

My theory is that the vac ball should be air tight and since mine seems to not be it is creating a tiny vacuum leak. When the engine tries to idle the extra air is causing it to idle a bit high until the ecm gets fed up and manipulates other factors (lets say spark timing for example) to drop the rpm to its desired idle speed.

[Anonymous]

If it is a vacuum part it should be air tight.

Mine isn't loose, but the hose that goes to it just plugs in and doesn't seem like it'd be really tight.

[jmgtp]

I just plugged the connection at the T harness. Made no difference with anything.

[pocket-rocket]

It should be air tight. Like you said, how else would it store vacuum if it wasn't? Anything smaller then a V8 uses a vacuum ball to "store" vacuum for use on vacuum devices (HVAC, cruise, ect.). The reason anything smaller then a V8 uses one is because V8's have a good vacuum (2 more cylinders then us to create vacuum), and any vacuum drawing devices could use more vacuum then the engine can create at any one time, so the ball is used to store vacuum, kinda like a capacitor in electronics. And actually, Aaron, the 92 doesn't have to be completely stopped before it drops down to 800 rpms. I won't be running at 10-20 mph, but if I stop slowley (like normal people, lol) it will drop before I have stopped completely.

[Anonymous]

I stand corrected.

MY 3.4 waits until it is completely stopped.

[brian89gp]

Mine was doing the exact thing, high idle and vacuum devices functioned perfectly. Turned out that the fuel pressure regulator hose had blown off.

[jmgtp]

I solved the problem with my car. Initially I thought it was the vacuum ball because when I used lung power to suck on the rubber line going to it I wasn't able to 'build' any vacuum so I figured it had a leak. I disconnected the hose and clamped it but the problem persisted. Eventually I thought of the throttle cables. Boy did I feel like a jackass when I found that the throttle stop screw was holding the plate open just enough that the computer couldn't compensate I though the ecm would be able to adjust timing and such enough to compensate... nope! I adjusted the scew and the cables a bit (I have a funky setup for the cables because I made the 91 cables work with the 96 manifolds - had to modify the cable bracket). Anyways... problem solved. The idle drops to 1200-1300 rpm while I'm rolling and then down to normal idle speed once stopped.

Note: I never reconnected the vac ball. I have not experienced any issues whatsoever with any vacuum related devices (cruise, hvac, etc) at idle or under load and this is with the -13* on the exhaust cams which surely negatively effects manifold vac at idle.... my opinion: you don't need the vac ball.

[pocket-rocket]

Mine was doing the exact thing, high idle and vacuum devices functioned perfectly. Turned out that the fuel pressure regulator hose had blown off.

The FPR line blew off of the MAP a while back on the 92, and it started stalling out all the time. That's strange that mine did the exact opposite.

[Anonymous]

I wish my stalling was that, but I have checked the lines to and fro the MAP so many times it isn't even funny.

[pocket-rocket]

Have you changed your TPS? I had to chang that once apon a time when trying to get the 91 to stop stalling.

[Anonymous]

Yah, that and the IAC and all the vacuum lines surroundign that area. It helped, but not enough.

I'm almost positive it is the fuel injectors. I'll be using the 96-97s when I get my independent throttle body setup working

[montessgtp]

Check to see what your iac counts are at idle... I had this problem corrected by SETTING your iac counts with the adjustment screw on your plenum...


Put car in drive , set the emergancy brake...
Let car idle to normal...
Turn the idle screw until your iac counts are between 8-15
Also make sure with your iac counts set to this that you still have 0 Percent Throttle
If you can not set the iac to that count that i would suggest a vacuum leak

My car will drop to 1000 rpms at like 30 mph n drop to like 800 below 20 mph. Take in consideration most tach are not acurate mine is like 250 rpms off.