Idle Stability/Vacuum WTF????, Little insight here please Options

[bsamps4]

]Check out this video. My idle bumps just like the vacuum between 550-700rpms. It does this after the car has fully warmed up. Cold start the vacuum and idle hold firm until the engine gets up to operational temperature.

Things I\'ve done:
full boost leak test, and repaired the leaks I found.
smoke test, and repaired the leaks I found.

My question?....what else could cause this? Sticking IACV maybe????

oh yea...it\'s a 3rd gen 3sgte. Fully built...etc...most of you are probably familiar with my build. If not it\'s in the my project section.

http://s1190.beta.photobucket.com/user/bsa...403873.mp4.html





This post has been edited by bsamps4: Nov 12, 2012 - 7:18 PM

[delusionz]

yeah thats very normal, it happens from time to time, usually blipping the throttle gets it back to stable.

for sure clean out your IACV with some carby cleaner, get all the grit out so it turns freely then give it some WD40 to lube it again

but yeah, this will still happen from time to time, nothing to worry about

btw that idle speed seems a little low, it should be around 900, so check your base ignition timing is set to 10deg in diagnostic mode

(when warm)

[bsamps4]

Good advise. I will double check the timing., but mine is also shaking like that a lot. I will blip the throttle and it will start doing that same crap again

It hasnt ever cut off on me at least...

This post has been edited by bsamps4: Nov 12, 2012 - 8:03 PM

[MotoFoo86]

With your idle that low it's no suprise it's idling roughly, before further diag get it idling right or you might end up chasing your own tail.

[bsamps4]

Id love for it to idle right, but what options do i have aside from using the idle adjustment screw on the butterfly?

[Smaay]

for sure clean out the IAC for starters.

[bsamps4]

Does the IAC affect idle even after warm up?

[enderswift]

Check the map sensor. My idle went to crap after I accidentally cracked the hose nipple. A little jb weld and the problem was fixed. If I remember correctly you have an FCD wired into it. I'd check that too.

It would explain why this only appears when your car is warmed up (it enters closed loop). Plus your guage is showing 20inhg, which is the same vacuum I get. So a leak isn't very likely.

Also it would take a lot for both bolts to loosen on the distributor, not to mention for it to then vibrate out of alignment without some kind of noticeable oil leak. However crazier things have happened so checking cant hurt

This post has been edited by enderswift: Nov 14, 2012 - 11:05 PM

[delusionz]

thats not an idle adjustment screw, thats a throttle return stop

as for the shaking - do you have polyurethane engine mounts?

the IAC is 3 wire, meaning 2 coil (power one side=closed, power other side=open, no power = not swayed either way) so its always in search of the correct idle speed, that **** pulses like a mofo - so it must be clean and free to move to be capable of good idle

and when setting your ignition timing, it has to be in diagnostic mode so the ECU doesn't interfere

[delusionz]

the IACV is plenty big to run fast idle up to 2000rpm, the throttle plate should always return shut, it has a little pinhole in it for vacuum release

[bsamps4]

Yes, I have polyurethane mounts. I actually disconnected my map clamp and checked the vacuum connection a while back and all was good. I'm thinking the
IACV may be my issue. I'm just not looking forward to taking it apart.