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Old 06-01-2009, 12:05 PM   #1
ch@0s
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Default Can an IAC valve act as a vacuum leak

Can an IAC valve act as a vacuum leak if it is not working correctly?
I have had my TPI apart 5 times now looking for a vacuum leak.
I have replaced every hose and connector. I have tried the carb cleaner method. I even smoked a whole pack of cigarettes and blew them in the plenum looking for it. When I run Datamaster my IAC counts are in the 100s. I have done the adjustment procedure but they did not go down much. The car runs and idles ok but it hesitates on acceleration. According to Datamaster its running very rich BLMs in the 108 range and at idle it hits 80 KPA .

I am thinking of joining the RedTornado club.
I haven't been able to drive my car in 8 months.
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Old 06-01-2009, 12:49 PM   #2
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I suppose it could act like a leak if the pintle does not reach far enough into the bore of the throttle body. Pull it out and measure from the machined flange (where the gasket goes) and the end of the pintle. It should measure 28 mm. Make sure you have the proper thickness gasket. I think you can turn the pintle to adjust it.
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Old 06-02-2009, 08:35 AM   #3
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Quote:
Originally Posted by ch@0s View Post
Can an IAC valve act as a vacuum leak if it is not working correctly?
I have had my TPI apart 5 times now looking for a vacuum leak.
I have replaced every hose and connector. I have tried the carb cleaner method. I even smoked a whole pack of cigarettes and blew them in the plenum looking for it. When I run Datamaster my IAC counts are in the 100s. I have done the adjustment procedure but they did not go down much. The car runs and idles ok but it hesitates on acceleration. According to Datamaster its running very rich BLMs in the 108 range and at idle it hits 80 KPA .
Regardless of working correctly or not, because it allows air in through a port aside from the throttle blade, it is, and can be regarded as a vac leak.

At operating temp. 100+ cts means the t.blade is too closed and won't allow the IAC to compensate properly (160 is max. cts. and in cold start only). Depending on idle rpm would depend on cts. that you should be seeing. If at approx. 850rpm on a modded motor, counts need to around 40 (a stock motor and idle rpm would be around 10-20 cts.). You will need to reset min air by turning screw clockwise which opens the blade and lowers counts. (unlike the book, w/data master running, turn min air screw *start w/a 1/2 turn, turn car off and restart the car, which will reset iac then see were you're at w/datamaster and proceed from there) this will also improve your off idle hesitation. The above needs to be done in closed loop at normal operating temp.

108 blm means pig rich, the ecm cannot, and will not comp. 108 period.....it needs tuning. Too big of an inj w/out tuning, cam changes, huge fuel pressure etc. etc. would be the usual causes when modding.

There is no way you should be seeing 80 kpa at idle even with a huge cam. 80kpa means low vac. at idle and with smaller aftermarket cams it should be around 40-50kpa. IF you're still at 80 after IAC reset etc. you will need to look at intake sealing etc. for your vac leak. With the car running take a propane (UNLIT !!) and point it around the intake sealing areas (runners, base, plenum, etc.), when you hear the idle raise that is your leak. You can also try a differnet map sensor....

Last edited by mseven; 06-02-2009 at 09:19 AM.
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Old 06-02-2009, 10:47 AM   #4
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thanks guys Im on it
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Old 06-03-2009, 09:19 AM   #5
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last night I replaced the IAC and it runs alot better
I sent a new datalog to my tuner and he is sending me a new tune.
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Old 06-07-2009, 11:01 AM   #6
jan-erik
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Hi.
I cannot understand that the IAC will act as a vacuum leak. Why? I think it takes the air from the front of the butterflies which makes all air through the IAC pass through the MAF regardless of it going though the butterflies or the IAC.
That makes the ECM register the amount of air and the idle will be high but stable . If there is a vacuum leak there is a difference in what the MAF register and how much is coming in to the engine and therefore the ECM via the O2 sensor will quarrel and therefore the engine can start hunting.
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Old 06-07-2009, 01:16 PM   #7
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It does not take air away from the TB blade. It is an add-on and works in realtionship with the TPS/throttle angle.
Basically it has several functions and will add or subtract air aside from throtle blade angle. The IAC acts as a: choke function (cts. add-on in park, neutral, drive , AC., dead bands, v.s. coolant temp. etc.etc.), aids in emissions, so that extra fuel doesn' t remain in the plenum to allow burn off (follower), provide some smoother transitions when coasting (follower), and maintain idle or stall function (in park and v.s. coolant), which are all add-ons. Because it is allowing air compensation aside from the throttle blade in essesence becomes a "controlled vac leak".

Last edited by mseven; 06-07-2009 at 01:19 PM.
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Old 06-07-2009, 03:31 PM   #8
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Quote:
Originally Posted by jan-erik View Post
Hi.
I cannot understand that the IAC will act as a vacuum leak. Why? I think it takes the air from the front of the butterflies which makes all air through the IAC pass through the MAF regardless of it going though the butterflies or the IAC.
That makes the ECM register the amount of air and the idle will be high but stable . If there is a vacuum leak there is a difference in what the MAF register and how much is coming in to the engine and therefore the ECM via the O2 sensor will quarrel and therefore the engine can start hunting.
I don't know is this has anything to do with it but my can is SD (no mass air) so it may be worse for me.
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Old 06-07-2009, 03:31 PM
 
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